installing the previous releases RPMs is actually a perfectly acceptable workaround for me. i do not notice any difference between the versions aside from this bug, so the improvements must be in things i dont use.
i had to downgrade my other device to fetch the RPMs with pkcon download, and then copy them over to my main device, and then install them with zypper --oldinstall.
both devices are properly upgraded, with just jolla-messages downgraded, and can receive MMS even with ‘download-mms-automatically’ set to false.
EDIT:
p.s.: i was gonna try ssu release & ssu ur, then download, then put it back, but that was too scary to do on my main. is there some way to download RPMs from other version’s repos that isnt scary?