Forget 'self defence' it is mostly nonsense when taught in 'self defence classes'. The best self protection is still to be aware of your surroundings and to avoid/run if possible.
Learning a martial art for confidence, for strength, fitness, better 'ownership' of your body. All excellent reasons though, so do it anyway, but don't think that self defence is something you will learn in any useful way.
I am a reasonably good 'club fencer' - and can hold my own in Sparring in friendly contexts - but I would be totally overwhelmed by a 'good fighter' who has real world or tournament experience of 'violence'. Real world violence is also a totally different tone. I can fence and get bruises and it is all fun and games, at worst a few days of soreness... but I have also been assaulted in the real world, both by strangers and my ex-wife... no meaningful injuries from any of those, but a *much* worse psychological and physiological response.
Do a sport that looks interesting and fun. My personal tastes led me to HEMA and swords*, but you might find something else more interesting to you. *And unarmed ringen/grappling with a martial origin - both armed and empty handed.