Not knowing what you actually want from life can actually be extremely unsettling, and actually very detrimental for your MH. I completely understand that. I'm awful if I don't have a plan. I need it to lead somewhere. I couldn't 'just' go for a run. The run needs to have a reason, either a speed session, an endurance session, recovery run. And lead to a goal. This applies to all aspect of my life. I get that fully and totally.
I guess your health is inhibiting you making plans, or aspirations or goals, and that's extremely debilitating mentally, in addition to physically.
It's extremely easy for me to say this, so please understand that's a big caveat as I'm a gobshite
, but your FiL's perception of you is HIS problem and not yours. Try talking to him at length about the things that you know well like politics and finance and see how he gets on. If he doesn't understand that there are many forms of intelligence that should be valued then he's the one losing out on so many interesting people and discussions. You are bloody interesting, I don't always understand your technical posts, but they are interesting to read as they teach me things!
I've got fed up over the years of trying to fit into others peoples boxes and be what they want me to be, although I've definitely been there and done that too (was badly bullied as a teen and that affected me for a long time in terms of confidence and standing up for myself, well into my 30's). This is me. You can choose to like me or not, but I have no control over that and won't waste anymore time trying.
Now, if I could bottle how I've come to that realisation and actually applied it to my life, I'd make a fortune. Possibly age? Who knows.
What a load of waffle that was, but all with the intention of saying, 'I get it' 