If you are on Android use the New Pipe app. No ads.

I recommend you use a yt downloader its hard to find one without the ads being broken on next dns so here u go : https://youtube-video.download/en1/

is there a way to disable ads in streaming services like tubi.tv or plex on android streaming boxes?

I want to add to what Mohit said (share video to AdGuard and YouTube Vanced).

If you use webpage in good browsers instead of useless apps you not only can block ads but you also do something for your privacy. Some services like Twitter and Instagram and even this website (help.nextdns.io not my.nextdns.io) have https://en.wikipedia.org/wiki/Progressive_web_application PWA . You will have icon and it will look like an app but is running inside the browser. Not all websites have this, last time I used, Facebook, for example, did not have it. But it was OK in mobile web browser. You can even use messenger if you change the mobile browser to desktop.

As for streaming without ads, the best thing I know is https://wwww.webvideocaster.com Web Video Caster. Once you get to know how to use it's amazing. I can cast YouTube for example on my TV without ads.