matrix.org allows 100 mb attachment. It is federated, which means you can move your data to your server if you like later. There are many clients and server implementations now and it is e2ee.
I dip my toes in regularly for the last two years. Every time I do, Matrix has been an extremely janky experience with negligible command of good UX principles. It's awful, and I'm only trying to use two devices.
If folks want to convince less ideologically motivated people to switch and support The Cause it still needs so much TLC. It's barely competing on table stakes features for a chat platform.
More importantly, it is indexable by search engines (if you use view.matrix.org). But it's not as simple to use as discord quite yet. I say this as a self-hosted matrix user, but it's not quite as simple to call someone else (until element call becomes a thing) or use custom emojis, to show a few problems.
If folks want to convince less ideologically motivated people to switch and support The Cause it still needs so much TLC. It's barely competing on table stakes features for a chat platform.