Gajim has been genuinely pretty unstable and buggy for me on Wayland (Sway) with lots of "crashing", in quotes because they tell me it's not crashing if I try to report it, but it's more like the windows are lost suddenly (this has improved over time somewhat at least, it used to be the whole client several times per day and now it's just the file picker, which can mostly be avoided). As for Conversations, mostly works great, if I had to complain it would be that you're forced to use relative timestamps with no way to configure them.

To compare Matrix and XMPP, I like that with Matrix you can edit messages that are as far back as you want, not just the most recent one sent from the same device you're on. Sometimes I fire off a storm of messages and then while I'm waiting for replies I go to read over them again and catch some things I wanna fix that I didn't see before. I also like that Matrix is a bit more distributed in that if the homeserver the room is on/from goes down, everyone else can still chat. I even have a group chat originally made on a now completely dead homeserver but we're all still happily chatting in it. I'm using both XMPP and Matrix daily, but Matrix is the one I got IRL friends and family on. XMPP seems more popular with people from fedi and the like, what you might call "internet weirdos". I have considered trying to convince more IRL contacts to get on XMPP, but I'm not sure they could handle another move, and I'm not sure I could justify it when it's not an objectively better across the board upgrade. When we moved people off Facebook chat or Google Hangouts, we were going from something proprietary and centralized to something free and decentralized, also there was encryption I guess. XMPP is kind of a sidegrade. Ideally it wouldn't be a full move anyway so much as getting them all to sign up on it as back-up comms, but again I'm just not sure they could be bothered at this point.

As someone in the exact same boat as you (a happy XMPP user for 10+ years, with family and friends there), if I had to name one, it would be group calls and overall calls being supported in Gajim. We just hyperlink to jitsi meet whenever the need arises, not a big deal at all.