The fix for this issue is now available in the latest update of InDesign – that is, InDesign 15.0.2.
Please update your InDesign application to get this fix.
Adobe InDesign team
An error occurred while saving the commentTommas commented
I am facing the same problems for months now ... after some time working with an Indesign document there is no more UNDO possibility and no more say or save as ... after working with previous Versions I hoped it will be fixed with InDesign 16.1 but still the same problem ... even more problems appear with no possibility to even start InDesign because no access to preferences. Even after 3 hours chat with an Adobe Specialist nothing could be done because it was impossible to install Indesign again after uninstalling ... the only way was to set up all new from a few days older Backup Version ... waste of time, plenty of extra work and still no solution available