I am looking for a YouTube alternative client, where I can ideally import my subscriptions, and possible even like or comment on a Linux computer. Does such a thing exist?
Liking and commenting isn't possible through any client to my knowledge. Freetube is a nice frontend app available on linux. Follow existing tutorials for how to export subs from YT then import your subs in the app.
I switched to FreeTube not long ago. It has a local account that is independent from Google or any online activity. Meaning it will save your watch history and favorites and other settings without having a Google account. You can easily backup your local profile.
And you can import your subs. If you want, you can also use a different API backend from Individous, instead the Local API from FreeTube itself. Individious API is even more private then the Local API, as it does not connect to Google directly. But it gets broken more often, so you have to switch the Individious instance from time to time. And and don't forget the integration of SponsorBlock. And I have a setting to hide watched videos, which unclutters my view of over 120 subscribed channels.
All good. But not all, there are couple of problems we encounter from time to time. The biggest issue is, that Google is attacking these applications and services, because Google does not like them. That means, sometimes FreeTube gets broken and you can't watch a video or something is just not right. Sometimes it helps to switch to Individous if there is a working instance. Just today got a new FreeTube hotfix release, because we encountered issues.
And you can't like or comment, as it is anonymous without Google account. For that, I have to login in my Firefox browser with my account and comment this way. It's a bit annoying, if that is an important point for you.
I also like that we can create multiple profiles, where each of the subscribed channel can be put under. Then select an active profile to only see Linux or Gaming related videos in Subscriptions view (Edit: or set settings being active for that profile group only.)
If you're looking for an in-browser alternative I'd highly recommend you take a look at the LibRedirect extension for Firefox and Chromium. It'll automatically redirect any youtube URL to your preferred alternative between Invidious, Piped, PokeTube, CloudTube, Tubo, FreeTube, or Yattee.
If you're looking for an external app and like using your terminal then ytfzf may be a good choice. I've briefly talked about it here. It will even allow you to search on Youtube (through invidious), Peertube, and Odysee if you so desire.
I've been using piped. It's pretty fast from my (limited) experience. It doesn't have the ability to comment, but core features like playlist creation exist. There's also an android app front-end available from f-droid called LibreTube.
I’ve been using pipeline on my Linux phone, works well. Though make sure to change the server to something other than the default because for whatever reason it doesn’t have thumbnails.