While there are ways to block ads on your phone at the DNS level (ie pi-hole), this means (A) you need to set up some hardware stuff, and (B) it will only work at your house. Which is great. But a more flexible solution is if there is a way around it... on your device!
This only works on Android (or de-Googled phones, I presume). What you do is download the F-Droid store on your phone here (it's easy - just click download and follow the install wizard). F-Droid is a repository (or "store" as in storage) of free and open-source software (FOSS). Then once you're in, download and install either NewPipe Legacy or SkyTube from the F-Droid "store".
Now if you go to those apps, you can watch Youtube, without the ads. NewPipe Legacy allows you to watch with picture-in-picture as well. So far, I've been a little frustrated I can't rotate for landscape viewing - kind of odd, but not terrible. If that's really a deal-breaker, you can go back to ad-land of the actual Youtube app, but that is just very annoying for me.
Soon I'm gonna play around with how to get "subscriptions" to work, but right now, as I use newsboat, I've got a natural alternative (for me at least). Using the Feeder app (also from F-Droid), I take the urls of my youtube feeds, and paste them into a Feeder feed.
To get a channel's feed url, what you do is click on one of their videos (on a computer). ONCE you have clicked on one of their videos, click on their channel, and copy that url. For example, the Majority Report homepage has the following URL:
https://www.youtube.com/channel/UC-3jIAlnQmbbVMV6gR7K8aQ
Having retrieved that, you will delete the part that says "channel/" and replace it with "feeds/videos.xml?channel_id=". You then paste the edited URL into your RSS feeder application (for me, Feeder). This will load the feed for that channel into your RSS feeder. Then you can go into that feed, click on a video, and at first, it will default launch videos in the Youtube app! To get around this, I simply disable the Youtube app. After doing so, if I click on a video, it asks if I want to open the video in NewPipe Legacy/Skytube or Brave - I pick the Youtube client I want, and then open it (if it asks if you want "background" or "pop-up" video, select pop-up).
I realize this is a lot of work - it works well for me given my main setup, but maybe not so much for others. So I'll be looking around to see if there are easier ways to get subscriptions to work. But for now, I thought that was pretty neat.