free people from proprietary gardens, yet FOSS has actually been one of the biggest creators of such gardens

Forgive the nitpick, but FOSS is not creating walled gardens, companies are. (After all, software has no willpower… yet)

Element (and other crucial components of the Matrix ecosystem) received many rounds of investments including https://element.io/blog/element-raises-30m-as-matrix-explodes/ (These are investments, not donations.)

I would not be surprised if the usual bait & switch lock-in mechanism happens here as well.

Software licenses cannot solve every problem and AGPL is still the best option.

There are many larger problems related to FOSS including freeloading, right of repair, surveillance, lock-in… and they require social solutions rather than new licenses.