Home page for the entire suite (in French) with some screenshots: https://lasuite.numerique.gouv.fr/
Code bases are on GitHub and they use English there: https://github.com/suitenumerique/
Dev handbook (in English): https://suitenumerique.gitbook.io/handbook
Not French and I can't say I personally tried deploying any of them, but I've been admiring their efforts from afar for a while now.
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 links to hand here.
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.
However, this doesn't help support the folks improving & maintaining Element (either its clients or servers), which is the actual upstream product that Tchap is dependent on. Just like donating to the W3C doesn't help improve Firefox, if you were operationally dependent on a Firefox fork.