Easily missed questlines

Recently picked up the game for the first time, took a bit of adjustment coming from very story / cutscene light games but really enjoying it now.

Have reached the point of no return, and I’m going round trying to clear up as much as possible in terms of characters / side quests before going for it.

I think I’ve done / am in the process of doing all the “main” character quests (i.e. the ones that result in trophies), but have no idea if there are interesting hidden side quests I’m missing out on.

So, please can people drop where I can find some of the easy to miss side quests that are very much worth searching out?