Normally if you turn off notifications in Settings it should work, but Windows 11 is kind of a mess with this stuff. What I'd suggest is going to Settings > System > Notifications and checking app by app - that's where the trick is, because some apps have individual toggles that don't respect the global settings. Also go into Settings > System > Notifications and completely disable "Banner notifications" if you don't need them, or add the apps that bother you to the "Do Not Disturb" list. If you're still seeing notifications after that, try uninstalling the apps you don't use directly from Apps > Installed apps, because some are pretty insistent and won't even respect the system settings.