it just isn't much fun for me anymore. I'm not even excited for Luigi's Mansion 3 which I was in love with the other two. I'm 25 by the way.
welcome to adulthood - where you have responsibilities and a job, and far less free time.
And the free time you do have is better spent doing things that are either more productive, or with your friends/partner/pet/etc. Instead of having say 30 hours a week available for gaming as a kid/teen.... your available time is far less (mine is like... 8 hours a week, tops - and that's neglecting the garden in my house, etc.
), and you do things like partying, recovering from hangovers, paying bills, extra-curricular study, etc.
It does "help" if your partner is also a gamer, as mine is, but even so, we don't spend a heap of time playing video games. So much other stuff to be done.
edit:
for what it's worth, i'm in my early 40s, and my gf is in her early 30s. we both don't game that much any more despite both being "gamers" due to time constraints.
Also, as above - gaming is largely pointless if you have other things to do. It's a distraction, a diversion to pass the time for the most part. Get out there, do the things in the real world, with real people (or pets, real world projects, etc.) - you'll get far more out of it.
You may find that different types of games are more accessible or more preferable now - twitch games that require a large time investment to master are out. I used to love Unreal Tournament, Quake3, etc. But don't have the time any more - and it's no fun just being owned by 12-15 year old kids who have 30-40 hours a week to practice.
Look for things you can sit down and play for 5-30 minutes at a time in smaller chunks. When you have downtime between real world things. Like on a train. Waiting for something or someone, etc. There are plenty of such games on the switch.
Right now for example i'm playing Shining Force on the Megadrive bundle for the switch. It's an RPG that has regular checkpoints that you can typically reach within 30 minutes or so and doesn't heavily penalise death/failure. I've been playing for a week or so and have just picked up where i left off to have a total of maybe 2-3 hours of play.