We do support the foundation: https://www.numerique.gouv.fr/sinformer/espace-presse/dinum-...

Yup, DINUM does support the Matrix Foundation, which is appreciated in terms of helping keeping Matrix itself alive and independent.

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.