If you'd prefer a swipe typing library under a truly open license, NLnet is funding [1] the creation of one by the HeliBoard [2] devs.
HeliBoard currently uses a proprietary library extracted from GBoard, which you need to add manually (since the app has no Internet connectivity out of principle), but they're asking for swipe data contributions, to be then distributed under CC-BY-SA 4.0, which'll be then utilized by their own open swipe library.
Check our more details here [3], [4] if you'd like to contribute.
... With the only caveat being that general experience of using Matrix is awful.
I second the other commenter's suggestion of using https://stoat.chat/ or as it used to be called: Revolt, which matches the "Opensource Discord" requirement perfectly.
This seems very similar to another open-source tablet effort, which went a step further and designed a Hall effect sensor-based tablet: https://github.com/pompyboard/pompyboard
The creator of it has showcased the prototype at an osu!* streamer's channel (since low-latency absolute positioning devices are highly desired for playing osu!): https://www.youtube.com/watch?v=v1afJ7OpacU
* that is osu! (sic) rhythm game, not to be confused with OSU universities
Thing is, these things are automated... Internally.
Which makes it feel that much more special when a service provides open access to all of the infrastructure diagnostics, like e.g. https://status.ppy.sh/
HeliBoard currently uses a proprietary library extracted from GBoard, which you need to add manually (since the app has no Internet connectivity out of principle), but they're asking for swipe data contributions, to be then distributed under CC-BY-SA 4.0, which'll be then utilized by their own open swipe library.
Check our more details here [3], [4] if you'd like to contribute.
[1] https://nlnet.nl/project/GestureTyping/
[2] https://github.com/HeliBorg/HeliBoard
[3] https://github.com/HeliBorg/HeliBoard/wiki/Tutorial:-How-to-...
[4] https://youtu.be/CyjumVTWtJA