Tools and workspace gone, CC 5.4.3.544

Here are the instructions from that link to locate the preference files so you can back them up and restore them if replacing them doesn't solve your problem:

If you want to to protect a backup copy, do this:

Start InDesign 2021 (or your older version)

Open Scripts panel (Window > Utilities > Scripts)

Right-click on the User folder, and choose Reveal in Finder (Mac) or Reveal in Explorer (Win)

This is a folder named Scripts Panel in the Mac Finder or Win Explorer. Go one level above this folder to the preferences file named InDesign Defaults. If you make a backup copy of this file, you can restore it (copy it back) if the original file becomes corrupt.

To reset manually, delete InDesign Defaults and InDesign SavedData files, and restart InDesign.

Here is the folder location for the InDesign Defaults:

macOS: Home > Library > Preferences > Adobe InDesign > Version 15 > en_US > InDesign Defaults

Windows 10: Users > UserName > AppData > Roaming > Adobe > InDesign > Version 15 > en_US > InDesign Defaults

Here is the folder location for the InDesign SavedData:

macOS: Home > Library > Caches > Adobe InDesign > Version 15 > en_US >

Windows 10: Users > AppData > Local > Adobe > InDesign > Version 15 > en_US > Caches >

I usually visit this Caches folder to delete the InDesign SavedData file (when I manually reset preferences by finding and deleting InDesign Defaults and InDesign SavedData), but you might need to go into the InDesign Recovery sub-folder and delete all the files inside if you are caught in a restart/crash loop.

Some say the keyboard method works better than the manual file delete method. In worst cases, some users delete all files under these two folder locations.

I understand you don't want to have to reset any prefernce customizations, but if the files are corrupt (and you'll know they are if ID starts behaving again after you replace them) you don't really have a choice. This is the most common rason for flaky behavior in ID.

Because this is a common enough problem I keep, and recommend others keep, a backup copy of the two files made from a known good set (i.e. jusst after you replace the prefs and re-do customizations) so you can simply copy a good set back when necessary. Deleting the prefs will not do anything to cause ID to stop working, it will just reset those things that you can customize under Edit > Preferences... to factory default and remove the data for the last saved state of the workspace and rfecent files list.