I could absolutely never work FT week in year out - I've worked FT a lot in the past, but it's almost always been non M-F 9-5. For example, 48 hrs a week in a homeless hostel (2x24-hr shifts), or three nights a week shelf stacking... I'm a night owl and would go mad (and almost have) with relentless M-F 9-5 work.
It's embarrassing in a way, and it's not something I say IRL as I worry it makes me sound precious - 'I can't possibly work 9-5 like other ppl!' But the times I've tried it, or have tried 'settling down' with a partner, it doesn't work.
However (and I'm only saying this in the hope it might give you ideas), I've set my life up so I don't have to work like that. I'm single and childless by choice, and the only property I've bought is a static caravan, where I stay in between bouts of travelling. (The travelling isn't as glam as it might sound; I've WFH for years, so basically just work somewhere else in the world for a bit.)
As above, I'm only saying this in the hope it might give you ideas; my life certainly isn't rosy all the time. I've had major depression since my teens, and often have sleep issues to the point I can't function. (This is mostly why I freelance/WFH.) Sometimes I'm lonely, and often I think it'd be lovely to have my own house with garden and be able to have pets, like pretty much everyone I know who's my age (mid 40s). But I decided in my twenties that for me, 'occasional loneliness is the price of freedom', and overall I'm pretty happy with my life. I saw a piece in the Guardian this week about ppl who've had 'gap years' after 60 - while I'm some years off that, it did make me think that I've set my life up as a permanent gap year. Which means I've had a few spiteful comments over the years, along the lines of 'Well it's OK for you, you're off to Thailand for six months'. But as I never point out, most people could do that if they really want to! But can't in real terms because of mortgages/kids.
The last straw for me was going into work one Monday when I literally hadn't slept at all the night before - I decided that sometimes being skint/ not having a 'career' job / not having a nice house and a few pets is preferable to that awful sick feeling every morning at having to go into work in a job I hate. After a few awful episodes of poor mental health, where I was suicidal, I now guard my mental health fiercely. Maybe you don't have to do the 9-5, OP?