The functionality of copying assets (scripts, tests, monitor profiles etc.) between projects is not supported by LRE (any version of LRE).
It is supported in ALM/PC12.x only when you've used the ALM client opening both projects in your IE browser.
This functionality was provided only by the ALM client which contained the related logic (code) .
As LRE / also My PC/ are using browser only - they do not have this functionality.
With the LRE 2020 you can ONLY Copy within the SAME PROJECT.
If you want to Copy to OTHER PROJECTS, the "Paste" button is DISABLED.