Since the 1.21.120 update when add on save locations were changed on Windows I have not been able to install non marketplace add ons without manually adding the BP and RP to the appropriate folders on my computer. I used to be able to just double click the add on file and it would import, but that no longer works.
Linked issues
duplicates 1
Comments 4
In version 1.21.120 and later, you must close the game before you can double-click the file to execute the import layer operation.
Duplicate of MCPE-227874
Yea I've also had a similar issue when I imported an add-on it would start the import and emediatly cancel it with the loading resource packs screen