Hi both, just to add my two cents as someone who's been through the whole process...
When I was choosing my A levels I had absolutely no idea what I wanted to do with my life, or even if I wanted to go to university, so I just choose subjects I knew I enjoyed (art, textiles, french and RS).
Ultimately, I decided in year 12 that as I was really enjoying the RS A level, I started applying for theology courses at university. I was accepted for Oxford and so got my degree in Theology.
I still didn't really know what I wanted to do careers-wise, but decided to apply for graduate schemes in the public sector. These are sort of like apprenticeships for people with degrees - they can be a really good way into different careers, and most don't require any specific degree subject as long as you have a degree.
I entered the NHS graduate management training scheme (a complete change from my Theology degree) and it gave me really helpful experiences and skills over the two years of the scheme. When I finished it last year, I got a job as a project manager in the NHS.
I guess what I'm saying is that it is completely fine not to know at your stage what job you want to have, and that choosing subjects you enjoy is a perfectly good way to do it. Even if ultimately you end up in a career that's unrelated to your studies, that doesn't mean they weren't valuable, as they will have got you to that point regardless.
Happy to answer any Q's if helpful. Best of luck!