honestly hashtags is 100% lemmy’s fault: groups/communities are “audience” AP field, lemmy some time ago aiming to be “more compatible with mastodon” made it so that posts in communities get automatically added an hashtag, and hashtags get sent into communities. this is honestly stupid and should be undone, you’d better aim your anger at lemmy devs.
regarding mentions, Twitter-like software needs them for addressing: lemmy implies that replies are addressed to replied-to user, other software doesn’t (you may want to contribute to a conversation without mentioning user directly above). if they don’t mention, you don’t see it, you’ll have to just deal with this. you could cook yourself a client that finds mentions in object “tag” and removes them from the body itself if you care this much
while “Could not decrypt message” is the n1 meme for matrix, i haven’t seen it happen in a long while, maybe a year. synapse and element x are quite good at this point, you should try matrix again
im not an element fan, company is a bit spoiled and sassy, but they stopped adding features and went all in on polishing recently. fair, as they’re trying to sell themselves for national deploys