some trustworthy alternatives to Mangadex

Not really, no… I have two sources that I turn to in last resort when Mangadex doesn’t have something and I can’t get it legally. First is Weeb Central (formerly known as Manga See). They have a mihon extension that works to sidestep ads, so I don’t even know how offensive their web ui might be. They do host direct scans of official releases though, so I would prefer not to link directly to them if possible. If you find a series on there that is being scanlated, then just link the scanlator’s site directly (cancerous ads and all, just give a warning).

The other source of last resort would be bato. I tend to avoid bato these because its mihon extension was broken for a long time and I migrated away from it (not sure if it works now or not). However, I do see several series that I read where the credits page says that the SL group uploads both to mangadex and bato. So, it might be worth a try.