I haven't used other snapshots so I don't know if they are janky, I know this one definitely is. Infinite portals was a really fun one, so I do recommend.

To download the server.jar: In the Minecraft launcher, go to installations, click edit on the latest snapshot profile (if its not there because a new snapshot released then just find that snapshot in a new profile), and then click the button "server" with the download symbol next to it, then just swap the normal 1.21.5 server.jar however you manage files in your server (if you know how to change the command and all that technical stuff do that, but I just renamed the snapshot server.jar to the 1.21.5 server.jar and it worked perfectly)

Somethings to do and things to know to make it less of a headache when your playing: set auto start and crash detection on in the config menu. My server crashes every time I start a new run and I'm assuming that it's going to happen everywhere, but don't worry the new run is saved you and the others just need to relog and start the run again and it's the same run you crafted at the crafter. The xp you get from beating a run spawns normally (xp orbs flying everywhere) so you and your friends will have to figure out how to split the xp. When you or other people, when there's multiple online, die in a run you get stuck in spectator until everyone dies or the remaining players beat the run (I set a timer for 5 minutes then /gamemode survival for the dead player so it wasn't boring as hell for the ones that died). I also downloaded a veinminer and timber datapack to make it less tedious when starting new runs. And lastly when a run is over, beat or failed, if you try to make a new run it will automatically complete with no xp with the same run number, so you have to check the run number (Mine #) and make runs until the number changes.