How to disable or stop Windows 10 update permanently?

I would not break the update services. A better long-term setup is to make Windows ask before installing and to hold feature changes while still allowing security fixes. On Windows 10 Pro, open Local Group Policy Editor and set Configure Automatic Updates to notify for download and install. You can also set active hours and use the Target Release Version policy so the PC stays on the Windows 10 release you choose. On Windows 10 Home, use Settings to pause updates when needed and set the connection as metered if you are trying to avoid large downloads on a limited network. Keep Defender and monthly security updates working; otherwise the machine becomes harder to support and riskier to use.