Oh yeah... I remember Windows behaving weirdly when I tried to copy some files with long names into a deeper directory tree. And it was just weird behaviour - no useful error message.

Windows in particular supports at the API level paths tens of thousands of characters long, much longer than Linux. The problem is applications need to explicitly support such paths using the long path syntax, otherwise they're limited to 255 characters.

Yeah I thought there was some way of doing it, but weirdly it was explorer.exe that was behaving in odd ways.

Great point I stand corrected

You expect the files to still be accessible using relative paths. What do you expect to happen if your cloud storage file path is 50 characters long and is mounted in a folder which is 4050 characters long when PATH_MAX is 4096?

The sync application itself can handle this using openat(2) or similar and should probably be using that regardless to avoid races.

Ah, I forgot that the maximum path length is usually limited by PATH_MAX, it's the path segment that's usually limited by the filesystem.

Point taken, although I still think it's better for cloud storage services to err on the side of compatibility, i.e. what's the lowest common denominator between Linux, macOS, Android, iOS from 10 years ago and Windows 7?