I've had several recent designs that I've been the author on, that when I share the working file can't be opened by other users. This has occurred with a company work design file and a personal project design. In both cases, these files were made with InDesign 2021 on Windows 10. The other users that tried to access my files were on Macs (unknown OS) using InDesign 2021 as well. This is problematic and damaging to workflows if other users can't open and work in files created by someone else.

PS. It is unclear if this is an issue between users on the same systems Mac/Mac or Windows/Windows, but has been demonstrated as a cross-system issue Windows/Mac.