Don't auto-restart for updates while someone is signed in — via Microsoft Learn

Group Policy

Open gpedit.msc (Pro, Enterprise and Education only) and go to:

Computer Configuration > Administrative Templates > Windows Components > Windows Update > Configure Automatic Updates (4 - Auto download and schedule the install) + No auto-restart with logged on users for scheduled automatic updates installations

Registry equivalent

Double-click a .reg file and confirm to merge it. Right-click → Edit first if you want to read it, which is always a good idea with any .reg file from the internet.

Apply

Windows Registry Editor Version 5.00

; Oddbyte.Me: Don't auto-restart for updates while someone is signed in

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU]
"AUOptions"=dword:00000004
"NoAutoRebootWithLoggedOnUsers"=dword:00000001

Undo

Windows Registry Editor Version 5.00

; Oddbyte.Me: undo Don't auto-restart for updates while someone is signed in

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU]
"AUOptions"=-
"NoAutoRebootWithLoggedOnUsers"=-

Same thing from a command prompt

Run in an administrator Command Prompt or Terminal.

reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU" /v "AUOptions" /t REG_DWORD /d 4 /f
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU" /v "NoAutoRebootWithLoggedOnUsers" /t REG_DWORD /d 1 /f

Undo:

reg delete "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU" /v "AUOptions" /f
reg delete "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU" /v "NoAutoRebootWithLoggedOnUsers" /f

Microsoft says this policy "doesn't work exactly as per description", was never made into a CSP, and can result in quality-update restarts never happening — so restart yourself regularly. On Windows 11 these policies may sit in a subfolder of Windows Update; use gpedit's filter to find them by name.