Thank you for your patience all this while; we really appreciate your support!
Our investigation suggests that one of common reasons for the problem is that certain software (mostly antivirus and other security applications) and browser extensions happen to enable “Secure Keyboard Entry” on Mac machines due to which some keys such as Shift key in this case do not perform the desired action in InDesign.
For now I request you to follow the below provided KB doc for the quick workaround of the problem.
In the comments section many of the users have confirmed that disabling Webroot SecureAnywhere (a security app) has resolved the issue for them. Please note that, the problem may not be related to a particular software; there could be a different application or antivirus which might be causing the problem by enabling Secure Keyboard Entry on Mac.
An error occurred while saving the commentKelsey commented
Yeah, what the heck! So annoying.