I’ve read books in which a character’s flaws are so subtle you have to dig through once more to actually find them.
You need your characters to be flawed. It’s not a choice. They must be flawed. A character without flaw is unrelatable altogether. (But I mean, if that’s what you’re going for- because sometimes it really is, go for it.)
Don’t be afraid to shove your character into a situation that might eviscerate them emotionally and mentally from the inside out.
Done and done.