LAN server suddenly not working?

My sibling and I used to play LAN minecraft together, both with 1.21.11. Nothing has changed (to my knowledge), but today it's stopped working. I am always the one to host it, and the world doesn't show up on the other computer's multiplayer list, and direct connection gives an "invalid session" error. I've tried disabling firewall temporarily on both ends, of course restarting both computers, and they are both on the same WiFi. I've got Windows 10 (ltsc, all updated) and the other computer Windows 11. Hosting on the other computer doesn't work either. None of the various fixes I've seen after much searching have fixed it, so any help is appreciated.