Thank you for reporting the issue. Our investigation revealed that the problem manifests in multiple use cases.
We have fixed the issue in some of the use cases and are currently working on the remaining ones.
Please update your InDesign to the latest version, id 14.0.3 to try out the fix.
We shall update here once we have addressed all the remaining use case
We appreciate your cooperation.
An error occurred while saving the commentMartin commented
M1 MacBook Air / Big Sur 11.4 / Everything in text box disappears when editing text in document created by somebody else in same InDesign version (16.4) but Windows edition.