NewPipe is a YT frontend that blocks ads, allows downloading, can run in the background and is generally great. It's a killer app for Android in my opinion.

https://github.com/TeamNewPipe/NewPipe

Firefox works fine on Android, and supports ublock origin and playing youtube in a background tab/with screen off. Couldn't speak to DRM as I've never used it on any platform.

On Android you can still patch the YouTube apk with Revanced and get rid of ads (and you can enable sponsorblock, etc).