Newpipe is the best client on Fdroid, but I don’t know if you can use multiple (or even any) account with it

Most open-source clients will by default have the option to block ads, which goes directly against the TOS and will be a quick way to get their API access shut down. This is why most open-source clients will avoid using the API in the first place, since they’ll get shut down. This means that connecting to a YouTube account is not an option.

What you’re searching doesn’t exist and will never exist.

You want to comment/interact with multiple accounts, and that can be done exclusively with the official app and the official website.

The reason is that if someone reverse engineers and spoofs a way to comment from a foss app, 30 seconds after the first release, some spambot asshole would immediately edit the code to send spam, and Google would patch that way immediately

Not really anything like this out there, Grayjay might work but I’ve never tried it. You could have two different ones, like NewPiped and Libretube, maybe?

Newpipe for Videos Innertune for Youtube Music - highly recommend this.

https://smarttubeapp.github.io/ On my Android TV.

Personally, I really enjoy LibreTube (Website, F-Droid link, GitHub). It is great for privacy as it proxies all traffic to YouTube through a Piped instance meaning you don’t have to connect to YouTube servers and your identity won’t be exposed to Google.

NewPipe (Website, F-Droid link, GitHub) is another good option, but it makes direct requests to YouTube. There are also forks of NewPipe like NewPipe x SponsorBlock (IzzyOnDroid link) which just adds a SponsorBlock integration and there is BraveNewPipe which has support for more video streaming plattforms.

Clipious (F-Droid, GitHub) is a pretty new app that uses the Invidious API to privately pull content from YouTube. I haven’t tried it out though.

LibreTube

Google killed off most YouTube apps some years ago, in favor of YouTube Red. Google stated those apps being in violation of the YouTube ToS, but even when those apps removed the violating features, Google would find new reasons for keeping them off the Play Store. Well, and then they would sell those supposedly ToS-violating features themselves, as part of YouTube Red, like for example background playback.

Since then, most YouTube apps are knowingly in violation of the ToS or at least not holding their breath that Google might decide so.
So, either they don’t use the official YouTube API, like NewPipe and LibreTube, meaning you can’t log in with those. Or they don’t put in too much effort, like ReVanced just being a mod of the official app, so that won’t have the features you want. Or I guess, they just risk it for quick profit, like Grayjay, but that will probably get shut down before they have such features developed.
Theoretically, a non-ToS-violating app can exist and could be distributed via the Play Store, but it would basically not be able to integrate any unique feature.

So, yeah, as others said, I don’t think this exists.
You could try some alternative methods like:

• Use two different apps, logged into two different YouTube accounts.
• Utilize an Android work profile to be logged into different accounts with different installations of the same app.
• If you just care about having different subscription feeds, use RSS feeds instead.
• See if a non-Google operating system is less shit at this.

Unfortunately I haven’t been impressed with the TRULY open source options. There are two KINDA open source options that I would personally say are much better:

• ReVanced is sorta open source, but it’s basically a tool to modify the YouTube app, which is not open source.

• GrayJay is source available, not truly FOSS. But it’s an excellent app and has been stable in my experience (especially impressive as it’s only a few months old).