cmd+z not working

cmd+z indesign not working. it will work when i first open the doc but switch off at some point. have to restart the software to resolve it. edit>undo also appeared greyed out and unclickablei'm running on macOS tahoe 26.6, and indesign 21.4.1. I have also disabled generative AI features in my indesign preferences. i have uninstalled and reinstalled the software and that didn't work, restarted my machine, reset my program preferences and nothing i’ve been trying seems to solve it. I have been dealing with this issue on and off for the past 8 months - it seems to happen randomly, but possibly more often on gigantic files.