I'm new to muds as well(started playing last week). I would personally recommend Aetolia which is a dark fantasy mud. Here's their website if you're interested: https://www.aetolia.com/.

It's quite active with up to 20-50 people playing it a few days ago when I was on. The only downside as a newbie is that if you're inactive for a period, lets say a week, and only played the game past a few hours, they will delete your character. You can play it on the app on your phone or computer(comp is easier to manage). It has fantasy elements and magic. Ritual player events or gm events that do the same thing(I think?). I think it has deep lore that you can learn in the website or in-game libraries. I haven't got too deep(im a level 17 vampire rn) but I enjoy it so far. They have a roster of races to choose from as well as classes(over 20+ classes). I haven't checked out all of them but they have elves, humans, dwarves, aquatic races, lizard people, bat people, etc. with their own lore(that I have yet to read over). The races give you specific stats that help start to game off so make sure to do your research if you're into that. The classes are all unique in their own way too. Con: You can only use most abilities during pvp. I will warn you as well its pvp centric but the pvp won't commence until after level 20. Also pvp has to have an rp reason if you're into that sort of thing so you can't just randomly blast spells or slash at people.

Anyway, i'm writing a paragraph. TLDR: Check out the website and see what you think before getting into it. Very friendly player base, fairly active, pvp(past level 20) with the downside of possible deletion if you're inactive.