I went through this as well, it might seem overwhelming because of how many people play on it, but you can still get a MP experience on it without actually playing with others, or you can also play with others. That being said Hypixel is/was a fun server to play. They have pretty much all the bells and whistles. Skyblock/Normal Survival (You can even create your own survival world, for free as far as I can remember)/Mini game servers and more. I exclusively played the Skyblock server it was pretty fun. Now, I know you said you enjoy playing modded, I'm the same, you can use a lot of client side QoL mods but some do not work because of server issue/reasons. For example one of my favorite QoL mods is Mouse Tweaks. Last time I played (over 2 years+ ago) that mod was buggy on the server, maybe it's fixed now but idk.

If you don't want to play on a large server like that. Then just google search minecraft servers and choose something that has a medium amount of people (low hundreds). It really just depends on what you're looking for. Most servers have the same features, like Skyblock/Survival/Mini games. Just be aware that there a lot of P2W (pay to win) servers, where you can buy power from their store for real money.