I wish Mastodon had encrypted DM's. I've been focusing on using Mostodon as my main place for media.
I can't find a Matrix client in F-Droid to use because when I turn off all of the anti-features, it seems Matrix is not an option to install something.
Have you not tried SimpleX yet? If not, I would suggest when the new release for 5.2 is in F-Droid you should install it. I could give you an invite link to message there but I don't want others on here using the link.
I'm registered with FluffyChat, it seems fine.