This point also makes me reject this. BUT thanks to comment about paper holder, I found out it has like a cap, so maybe inner part will be flattened. I’ll see it later.

It’s a good point! I just check paper holder and it has slightly moving cap. I will try disassemble it to see it inside. It def not a toilet paper holder, but it should be a ring towel hook then!

Thank you! I agree it’s the best guess. It was on a face level on the edge of the tub. So it could be used both inside and outside of the tub. But what makes me doubt: most pivoted mirrors have the moving part between two fixed brackets. And of course no similar images on the internet.