Please tell us what operating system (exactly) you're running.
Did you remove your previous version of InDesign when you installed the new version? If you did not, you can try using this command: Edit > Migrate Previous Local Settings.
OK, try this. You want to locate where your InDesign 2020 (version 15) stored your custom workspaces. It should be in this path:
Mac/Users/[your username]/Library/Preferences/Adobe InDesign/Version 15.0/en_US/Workspaces
It's an XML file. You should be able to copy it to the same path for "...Adobe InDesign/Version 16.0..."
If you're new to this, the user Library file is hidden so use this to make it show:
Thanks, that helped, I just still have to reselect everytime Indesign restarts it isnt defaulting to it.