Hi! Welcome backl
None of us are getting any younger, and this is a fairly common question.
There isn’t a single clear answer.
When you get to raids and M+ dungeons, the devs keep adding mechanics and junk on the floor, that affects everyone. OTOH, the addons used get smarter and smarter as well.
I think you will remember DBM Deadly Boss Mobs, but you will now find that WeakAuras, together with all the libraries people make for various warnings and conditions will help you keep up. You can even download whole UIs from streamers and YouTubers, for example https://www.youtube.com/watch?v=ulkQhuef5SU
Now, for classes, Hunter, and specifically BM, is the canonical example of a class that is least affected by mechanics, that can cast on the move from range.
But I still think that how you enjoy the class has a lot to do with how easy the class is for you as well.
Here is a recent thread asking specifically about a class that isn’t too fast. It may have something useful for you:
My best advice is to look at YouTube for each class and spec you are interested in; it’s the best way to get a quick sense of what it does. Make sure you are looking at a Shadowlands take on the class, ofc.
If you have bought Shadowlands with the boost, you have the option of taking a trial character for a spin at 50, and when you have narrowed it down to a suspect class, that is worth doing, just to see how you feel with it at high level. But levelling is so fast in Shadowlands anyway that it’s not the problem it once was.
Do please consider what realm and faction you would like to play on. Choose your realm carefully, as one in which your faction is in an overwhelming majority. You can sort by faction population here https://www.wowprogress.com/realms/rank/eu/lang.en to get a shortlist, and there are other threads on this forum about realm suggestions.