@kagan you can comment on the github source code repository (i believe it has a discussion forum) but historically those efforts usually do not get much response
however, many admins control the codebases for their instances and can make desired changes themselves. the difficulty is coordinating that work so it isn't an undue burden and doesn't introduce maintenance costs down the line
my advice for users would be to express feedback in a polite and understanding manner to your admins, with the understanding that they are probably also frustrated. you can also tell them to me! (i'm trying to compile them for a blogpost). my post was addressed to admins because i expect them to be most knowledgeable about the software and how it has changed but i'll take comments from anyone
(i am not affiliated with mainline mastodon development and am just trying to coordinate patches, as above)