Forge: 32.0.108
restrictedportals-1.16.1-1.1.2.jar

Disabling Restricted Portals allowed the server to complete loading, and created a new world as normal (although I received a warning saying the world was created with Restricted Portals enabled, so things might not work as expected). I then tried re-enabling RP and restarting the server, but it crashed during loading once again. Logs linked. Thanks!

crash log: https://hatebin.com/zritovlkyu

preceding lines in latest.log: https://hatebin.com/yvtawahouz

Regarding my original comment: this error is what I see sometimes when I forget to remove a client-side only mod from the server, but surely Restricted Portals is server-side, yeah? Considering it creates a datapack and the main intent of the mod is to prevent people from rushing through the game in multiplayer, I would assume so.