I. The Microsoft official way to stop all automatic updates
Press WinKey+i > Update & Security >
Advanced options (in the right pane).
Under Pause updates, it says :
Temporarily pause updates from being installed on this device for up
to 35 days.
When you reach the pause limit, your device will need to get new
updates before you can pause again.
One thing you could try – after 33 or 34 days – is to pause for
another 35 days (without prior resuming of the updates) and see
what happens.
I haven't tried it myself, so I cannot tell if it works.
The reason I don't use the Microsoft official way to stop all
automatic updates, is that I use my own unofficial way,
which I will dedicate the rest of this answer to.
Disclaimer.
If you try any of the tips below, it's all at your own risk.
II. My method to permanently stop all automatic updates
My method: block the wuauserv and WaaSMedicSvc services
by renaming them in the registry.
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This has served me well for many years.
2
It's the closest I can get to that on/off switch that
Microsoft stubbornly refuses to give us.
For more details on how to do this, read on.
1. Precautionary actions. (Don't skip this – better safe than sorry!)
Before moving on, I strongly recommend saving a copy of the Windows
Services registry settings.
Press WinKey+r, type (or paste) regedit and
hit Enter.
In the navigation bar, paste HKLM\SYSTEM\CurrentControlSet\Services
and press Enter.
Right-click Services and choose Export.
Make sure you save the backup .reg file in a safe place where
you will remember how to find it – should you ever need it.
Expect the file size to be just below 8 MB.
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The most vulnerable registry key in this context is :
HKLM\SYSTEM\CurrentControlSet\Services\wuauserv
so it's a good idea to also export that key into its own .reg file.
Remember where you keep it!
2. Block the wuauserv and WaaSMedicSvc services in the registry
Next scroll down to :
HKLM\SYSTEM\CurrentControlSet\Services\wuauserv
Right-click wuauserv, click Rename and add the suffix
-BLOCKED!! so that the key's new name becomes wuauserv-BLOCKED!!.
Likewise, rename
HKLM\SYSTEM\CurrentControlSet\Services\WaaSMedicSvc
to WaaSMedicSvc-BLOCKED!!.
Now press WinKey+i, click Update & Security,
and then Check for updates.
Expect to see an error as in the screenshot below.
Possible error numbers include 0x80070002, 0x80070424,
0x80080005, 0x80040154.
If you see this error, it confirms that you have successfully disabled
Windows Update in the registry.
The error was immediate when I tried this, but you may have to
restart the computer for the change to take effect.

How to enable Windows Update again
When you later want to enable Windows Update again,
just rename the registry key back to its original name wuauserv.
(You shouldn't need to rename/unblock WaaSMedicSvc-BLOCKED!!.)
Before renaming back, you have to delete the wuauserv key if it
exists.
Don't delete wuauserv-BLOCKED!! or WaaSMedicSvc-BLOCKED!!
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After renaming back, you need to make a software restart
(WinKey+x followed by u and
r) to activate Windows Update again.
Note!
A hardware restart – just shutting down and then restarting by
pressing the physical power button – will not start Windows
Update.
3. Windows Update may display as if it works even when it doesn't
The surest way to know if Windows Update has suddenly started to
run again (without your consent), is to go to Settings >
Update & Security > Windows Update.
If you see an error, then Windows Update is still successfully
blocked.
But even if you see a green checkmark as in the screenshot below,
Windows Update might still be blocked.
You could click Check for updates to see if there is an error
or not.
However, if there isn't an error, Windows Update will start to
download any new updates and install them on the next restart.
This might not be what you want.
To gain more control over what updates to install,
run wushowhide.diagcab
which allows you to prevent (hide) any updates that you don't want
to download.

4. Optionally also block the UsoSvc registry key
If you take no further action, expect Windows to automatically and
silently recreate the wuauserv and WaaSMedicSvc registry keys
as shown in the screenshot below.

From my experience, this is not enough to make Windows Update run
again.
Still, if you feel uncomfortable with the wuauserv and
WaaSMedicSvc keys being recreated (I do), then you can prevent this
by also blocking the UsoSvc registry key.
As with the other keys, just rename it toUsoSvc-BLOCKED!!.
As opposed to the other two keys, I have never seen the UsoSvc
registry key get recreated.
If you do this, and then go to Settings > Update & Security >
Windows Update, now expect to see :
Something went wrong. Try to reopen Settings later.

5. Check the status in services.msc
To take a look in Windows Services,
press WinKey+r, type services.msc
(and hit Enter).
Sort by name, look for Windows Update and double-click that service.
If the Service name is wuauserv-BLOCKED!! (or you get an
error), things are looking good.
Also check in a similar way that Windows Update Medic Service is
blocked.

^ click to enlarge
6. Don't run System File Check (SFC)
Don't run SFC unless you first restore Windows Update!
I once ran sfc /VERIFYONLY with the result that the
Trusted Installer
hijacked my laptop for about 45 minutes. (!)
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7. Remember what you changed!
One day you may find yourself wanting to undo the changes you made
here.
To reset your computer to a normal state (one in which Windows Update
functions normally), there are two keys to reset in the registry.
Press WinKey+r, type (or paste) regedit and
hit Enter.
In the navigation bar, paste :
HKLM\SYSTEM\CurrentControlSet\Services\WudfPf
Right-click wuauserv-BLOCKED!! (you should see it on the second
last line in the Registry Editor).
Rename it to wuauserv.
Next scroll up to :
HKLM\SYSTEM\CurrentControlSet\Services\UsoSvc-BLOCKED!!
and rename that key to UsoSvc.
If you press WinKey+x followed by
u and r to restart the computer, expect
Windows Update to be fully functional again.
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8. I recommend disabling System Restore
I recommend disabling the System Restore feature because when it
kicks in, it can (temporarily) make your system slow and unresponsive.
– System Restore may prevent you from using your computer
for about half an hour or even longer.
That's why I disable System Restore altogether.
Press WinKey+r and paste
systempropertiesprotection and press Enter.
Click Configure... and check Disable system protection.
Click OK twice.
9. What do wuauserv, WaaSMedicSvc, UsoSvc stand for?
I guess the letters in wuauserv stand for windows update
automatic service.
WaaSMedicSvc is somehow short for Windows Update Medic Service.
And UsoSvc stands for Update Orchestrator Service.
References
1 Never, ever run sc delete! – It will destroy your registry.
2
For example, in 2018 I updated to version 1803 (build 17134).
I did not let Windows Update run again until April 2022, when it
installed version 21H2 (build 19044.1682).
That's almost four years without a single update.
3
You can store the .reg file wherever you want.
Personally I store it in
C:\Downloads\Win10\RegBkp\HKLM\services
under the name HKLM%SYSTEM%CurrentControlSet%Services.reg.
4
If you delete it by mistake, I sure hope you still have the backup
I asked you to save by exporting to a .reg file!
Deleting the key is exactly what sc delete does.
That's why I advise you never to run it.
5 Holding down Ctrl+Shift makes the
command prompt open as administrator.
6
I tried disabling the TrustedInstaller by replacing TiWorker.exe
with an empty file, but that's not an option.
Windows cannot even restart normally when the the TrustedInstaller
is turned off.
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If not, let me know in a comment below.