One thing I just recently learned - NewPipe can cast to Kodi, but it needs a bit of setup.

First, you're going to need kodi running somewhere (FireTV Stick, Android TV, ...) and (currently) update the YouTube Addon to the latest Alpha.

(I installed it via the following repo: http://ftp.fau.de/osmc/osmc/download/dev/anxdpanic/repositories/repository.yt.testing_unofficial-2.0.5.zip )

Also, you'll need kore or yatse installed on your phone / tablet.

Then you'll need to allow remote control in the kodi settings for the app you just installed...

And lastly you'll have to go to the NewPipe settings (Audio/Video) and toggle "show >play with kodi<".

So... It's quite a bit of work. But I guess if you're using NewPipe, you're not adverse to some fiddling.