[mathisonturing]

Android has app system level options in the settings to disable WiFi/mobile data.

I tend to use that, and use Netguard as a fallback because the latter has an off by default config incase I forget to disable it for new apps.

Netguard on its own is insufficient because sometimes you'd need to use an actual VPN (which turns off Netguard)

[infthi]

I've had those options on multiple OnePlus phones, but they were not present on multiple Pixels. Since Pixels are usually sold as "AOSP experience with Google flavor" are lacking this feature - I am not sure if that is that feature comes from AOSP or is only present on OnePlus phones.

[jeroenhd]

I've generally found them on most Android phones, but they're all over the place in the settings. On my current phone they're not in permissions, or connections, or internet setup, or security, but they're in the app details screen.

I've also seen the toggles placed in the data usage graph, the other, older data usage graph you can sometimes find via a workaround, and in a separate app that pretends to be one of those system storage optimizers.

I'm sure Android supports it at the system level but how you get to those settings is anyone's guess, really.