This isn’t a Roon issue but rather how Linux interprets non-ASCII characters–ö is two characters not one–on the filesystem. Unfortunately for you MacOS and Linux interpret them differently and it would seem that the folders were created on MacOS.
It’s the difference between U+00F6 (ö) and U+006F (o) plus U+00A8 (¨).
For interoperability it is better to remove these characters in filenames (and retain in metadata.)