So the intrusive thoughts – are they like some nutter wandering into your head and banging on about suicide methods etc, rather than you yourself feeling “this is all terrible, I want EVERYTHING to go away”?

Probably still something to be cautious about. (I got the suicidal nutter in my head thing in my late 40s & HRT fixed it for me which shows it clearly had a biochemical component).

You’d be surprised by how much dumb stuff like good diet, 8h sleep at the same time, regular exercise and half an hour a day talking to family & friends can kick misbehaving thoughts and feelings back into shape, plus a bit of mindfulness, which can be as simple as telling yourself, “FFS me, put down the phone for 5 mins, you know it doesn’t make you happy!”.
Lots of us don’t get our heads on right until our 30s or 40s mind so you’re not particularly odd if that helps?