I'm going to start with the positives. On paper, you sound like quite a catch. You are active, ambitious, compassionate (choice of profession), attractive (probably - based on hobbies), personable (wide social circle), and looking for a serious, long-term relationship (rather than a FWB/fling).
I'd love to have a partner who I could share some of my hobbies with (traveling, off roading, rock climbing, mountain biking, boxing, weight lifting etc).
This, combined with the fact that you "just don't know what to say or do during dates", I think you might be best off meeting women directly through your hobbies. Are there moutain biking clubs where you are? Off-roading meet-up groups? Your lifestyle and interests are very much on the "active" side of average so you are not likely to get on that well with someone you just randomly met on campus or through friends. Don't go for a coffee on the first few dates, go for circuit training together (or whatever).
The two things I think could be holding you back are these:
1)
I usually prefer to listen to people rather than talk much about my life, and when I am forced to reveal things about myself....it's not very exciting
As a woman, a guy who doesn't talk about himself much on the first date is grounds for saying "no" to a second date. A date is like an interview that goes both ways: you're trying to figure out if you like her, but she is also trying to figure out if she likes you. If you don't give her anything to do on, the answer to that defaults to "no". Your aim on a date is not to be exciting - it's just to get to know the person and let them get to know you. You like travel? Talk about the last place you went and what you liked about it. "I like travel" covers a broad spectrum between "I enjoyed backpacking through rainforest trails for two weeks without WiFi" to "I enjoyed getting fucked up on eccies in Magaluf" - she has no way of knowing which one you mean when you say you enjoy travel, unless you tell her.
Additionally, a reluctance to talk about yourself is something that can come across as a bit of a red flag. Someone who doesn't want to discuss even basic things about themselves is likely to also be quite emotionally closed off and have a hard time navigating conflicts in the relationship in the long term - which is exhausting for the other person.
2)
pretend to be interested in something that I am really not interested in (which is very stupid and childish...I know)
Yeah, that is pretty childish actually. You're obviously going to have different interests, but there's a spectrum between "wow, I really don't care" and "wow, that's my interest too!" For example, I'm not interested in dirt biking. But if I was on a date with you I might still ask how you got into that, and what a normal day dirt biking looks like, and isn't that awfully dangerous? And hey, maybe you'll take me out on the track one day and I might enjoy it.
Good luck to you, I'm sure you're not "undateable" by a long shot, you're just out of practice - and maybe with all the lifestyle changes in your 20s it hasn't quite sunk in yet just how dateable you actually are.