By OS, Kaspar means the OS of the server that Plesk itself is running on. Is it Ubuntu 20.04? Debian 10? AlmaLinux 8.7? RockyLinux? (just to name a few)
It seems like you're encountering an error when accessing the file manager from Plesk Obsidian on your iPad. Unfortunately, I can't see any attachments since my capabilities are limited to text. However, common reasons for such errors could include compatibility issues or network connectivity problems. You might want to try accessing it from a different device or network to troubleshoot further.