Fjord Launcher Unlocked is probably the best there is. Has authlib-injector support out of the box, retains FTB modpack support, and is patched to remove MSA checks.
Also for players on your server you should recommend people use No Chat Restrictions in case they still wish to use Microsoft accounts for whatever reason. I feel like maybe that mod should be installable on the server so you can require players to use it, but currently it doesn't do anything when installed on the server.


