The internet just isn’t a good space to spend a lot of time. It’s mostly corporate controlled and they’ve found anger drives interaction online so most things you read are designed to be upsetting. I’ve drastically cut down on my internet usage over the last few years and while I do spend more time doing things I enjoy, due to not being online, I’ve found that going back on reddit or something similar can send me right back into a negative headspace for the rest of the day like when I was online more. I just think that most parts of the internet are miserable places to be.
I don’t remember it always being this way either. Back when small formus were the norm I found the internet to be much less hostile overall. Not that there weren’t jerks and chuds online back then, but there wasn’t the profit incentive to drive engagement over all else
I have a very similar experience as you, using the internet less as recreation and more as a tool definitely helped my mental health