Matrix is a protocol, unlike discord. The problems often come with the different clients. I personally suggest fluffychat wherever I go since that is the most usable in my experience. Element I have installed as a backup on all my devices if I need to troubleshoot.

Same as with apple‘s „iforgot“ service: the privilege of privacy comes with responsibility. You must either take care of a couple things yourself or pay someone to do it. On discord, a huge margin of people pays with real money and the rest with their data.

To the topic: Matrix rooms have a version and the server you make them on matters a lot. Therefore I would stay on org if none of you know your way around. If you have skills, make your own and configure it in the most non individual way possible for maximum compatibility. If people cant join even when you invited them, you might have to check if the servers each federate correctly. If not, switch servers or tell your admin.

Edit: you‘ll probably get advice at !matrix@lemmy.ml