While not perfect, whenever people talk about Discord alternatives I have noticed no one mentions Steam Chat. It pretty much has the same features and drawbacks as many of the other suggested alternatives with the added benefit being most people already have accounts.

Edit: One of the biggest problems I have found with finding alternatives (besides finding an alternative that has screensharing and VC for mobile users) is finding one my friends are receptive of. Matrix, Stoat, whatever else my friends are not interested and seem they would rather just try and trick the Discord verification shit. But Steam Chat they actually considered and seemed fairly interested once they found out what features it had. The fact most of them already had Steam accounts was a major reason why they were willing to consider it.