Okay, so I have been out of the loop for some time now and I noticed how my old mods and custom songs don't work for Beat Saber anymore.
I discovered they now allow custom levels and that those use .dat files instead of .json.
On bsaber.com I can download songs, but I found it more comfortable to browse inside of the game. What is the current go-to mod to do that? IPA and Beat Saber Mod Assistant haven't been updated for some time and with IPA the game crashes on startup.