Tube Archivist is great, as long as you don't mind waiting a bit to watch stuff. As far as I know Grayjay is still working fine.

Is it possible it was your Goggle TV that showed the ad?

Are these youtube ads or are you saying the app itself is displaying the ad? No mention of it yet on github.

I'd highly recommend giving TizenTube Cobalt a try. It's really solid and I havent had any issues so far.

This also happens to me, using the Smarttube flatpak, I think that it's a "feature" from the youtube tv original app, and it bleeds into Smarttube because what it does is faking being the original youtube tv app with some extra modifications.

Edit, I am using VacuumTube from flatpak, not Smarttube, but it's the same concept.