Earlier quoted context omitted.
Hmmm not entirely true. The text chat of their suite is simply element.io (matrix) and they're paying them for development. Visio does seem built from scratch but I wonder if it's a temporary thing until element is feature complete with their move away from Jitsi. You can find more about la suite on their website and the opendesk one (German project using mostly the same software). Unfortunately I don't have the link…
Tchap (the chat part of the suite) is indeed a fork of Element. Unfortunately they haven't funded upstream development for many years (otherwise both Element and Tchap would be much much better!) Visio (aka meet) began in parallel with Element's work on MatrixRTC and Element Call. Hopefully the two can converge, given they are both built on LiveKit.
How much better could open source alternatives to Teams be in this moment if only 1% of what Europe paid Microsoft for Teams went to investing in open alternatives?