alt Hacker NewsMMS has terrible limitations, in both file size and media resolution.
RCS has replaced MMS as a protocol back in 2008 and it's only now gaining traction. Many carriers have shut down their RCS infrastructure half a decade ago, though, so they're not exactly jumping on the chance to turn it back on.
I enabled RCS on my Samsung S21, but had to disable it after a day or two. It just didn't work reliably.
But yea MMS sucks, would be nice with some common cross-platform alternative that worked well.