I don’t have a Pixel 8 but that sounds highly unusual. I suspect you’re right, maybe the option didn’t exist in the same way on Android 14 and so it’s copied over in a weird way.
I don’t know a way to fix them other than just updating them all one by one. In recent Android versions the app can prompt you if it’s missing the settings so it should be pretty safe to just disable it for everything that doesn’t obviously need background usage.
Android by default does remove permissions from unused apps, and the run in background permission is one of the ones it will remove. It doesn’t say on that page but I think the threshold is 3 months.