Windows 10 is rebooting against my explicit will in order to install updates

You must have 4-Auto download and schedule the install enabled in Computer Configuration\Administrative Templates\Windows Components\Windows update\Configure Automatic Updates policy to have No auto-restart with logged on users for scheduled automatic updates installations option working.

See this table:

Read more detailed here, in Delay automatic reboot chapter:

Manage device restarts after updates

Windows 10 does what it wants, not what you want.

Windows 10 will change any settings at any time by itself when updates install.

Windows 10 will disable drivers and devices considered incompatible with it, even if they previously worked.

That said, on Win 10 Pro if you really want to disable updates, make sure the update service is permanently disabled.

Additionally, disable it's permissions to restart.

With those 2 properly set, you should be fine.

In the case of wireless connections, you can 'cheat' by enabling Metered connection. That will prevent auto-downloading of updates.