I don't know if this will help everyone with this problem, but I restarted my laptop and now I can open the project without a problem. There were also discussions about this issue a few years ago on Jetbrains forums, so you might find something useful here: https://intellij-support.jetbrains.com/hc/en-us/community/posts/360010604480-WSL2-specified-path-cannot-be-found
https://youtrack.jetbrains.com/issue/IJPL-2327/WSL2-specified-path-cannot-be-found