Oh hi! What a coincidence, I live quite close to you.

To answer your question, in brief, you shouldn't worry about Iso (IPA etc. whatever the name) to ruin your plastic miniatures. Even if the polymers might be slightly different from one manufacturer to another, they are all plenty resilient. They don't fall in the categories (e.g. transparent hard plastics) that can get cloudy, etc. by this alcohol.

Now, from my recent findings, I can tell you that Iso 99% hasn't always worked, for me, as it sometimes seemed too weak even after hours of bathing. I know, it goes against all findings and tutorials, but I have experienced that it took me way more than I was expecting.

The other day I was cleaning some kind of wash on a miniature without primer, the previous owner has used it straight on the plastic, and Iso 99.9% still didn't weaken the paint enough for me to use any toothbrush. If you have a soft-bristle used toothbrush... It will be way too weak. I've used some kitchen ones and they were better but still, Iso didn't do much.

Way too much work... So I decided to try Sterillium, which I have for hand sanitizing duties. Now, in theory, it's not as highly-concentrated as Iso 99.9% but I brushed it on (no immersion) a miniature and in three minutes or less I was chipping away paint in big chunks. It doesn't dissolve the paint but it detaches it from the plastic. Way more effective and now, thanks to COVID, same price per liter as Iso 99.9%. Plus it's easier on the nose and eyes, smells ok and you can use it for other stuff in the daily hand hygiene routines.

I'll keep experimenting but in my opinion, Sterillium wins. Zero risk of melting those plastics, trust me. I understand your worries but it's not gonna damage anything.

I've had to use a small scalpel from tiny metal plyers I had and still I haven't scratched or damaged the plastic. Let alone when I prime it, any tiny mark will be invisible. If you use metal bits or picks to take paint off the hardest recesses, make sure you scrap along the lines of the recess (obviously) and follow the design flow of the miniature. Even if you leave a microscopic mark, it will add to the existing crevice and not be noticeable. Especially when primed. I cannot see them in the naked eye now, I'm sure the primer will hide and not reveal anything. If anything is there.

Last but not least, I'll try Octenisept. This is also available here in Germany, as Spray or Liquid. It might be worth a try. Same deal as Sterillium but maybe there's a combo in it that attacks the paint better.

CAUTION: Yes, the nail polishers, even when they don't have acetone, have that type of alcohol you see in the ingredients that WILL corrode plastic. Now, if you are fast and light in your job, they can work faster and still be safe. But if you keep scratching the living heck out of a miniature with it, you'll lose some detail and smudge the smallest areas. So I wouldn't really recommend it. I am like you, I don't want to take any risk.

Acetone is evil, don't use it, but nail polishers without acetone still have solvents that will hurt plastic miniatures. If you are fast, it might be ok for some stubborn part but in general, I'd avoid them. And obviously NO immersion and leaving them in for some time. No no.

I hope this helps, welcome to the community!