On Android, there are a number of solutions, like NewPipe (YT client) and Seal (downloader).
Minus smart TVs, this seems like the point of the policy change. (And even on the TVs, if they're watching without paying while blocking ads, that's purely a cost centre.)
Your comment reads as if you feel that YT has some sort of obligation to continue letting 3rd parties make money from the work of YT without any compensation.
All device manufacturers do have agreements with Google about support for their devices and such agreements can very well be for 10+ years or even for lifetime of the devices.
PS: Actually 10 years ago when Windows Phone was a thing Microsoft has tried to make their own YouTube client without agreement with Google and it was killed by Google almost immediately.