@cy @annika It's still probably Matrix under the hood.
For those unfamiliar with it, there are loads of Matrix networks, private, public networks.
I was trying to match the screenshots with known Matrix clients to verify, problem is there are too many now. Think we can rule out text only ones but, with multiple mobile and desktop OS versions each that's a lot to check:
Element
Element X
FluffyChat
Nheko
Cinny
Fractal
Quaternion
gomuks
Hydrogen
NeoChat
SchildiChat
Ement.el
Tammy
iamb
chatty