You need to look for the directory in you UE50EA. Mine is
where MegascansPlugin contains the code for the plug in.
If the install was terminated early you could try deleting the C:\Users\Owner\source\repos\UE50EA\Engine\Plugins
“MegascansPlugin” directory and wait.
Reinstall as described above in the first article
Did you login and answer all the questions about paths to the UE50EA installation?
Go back into VS2019 and rebuild the source of UE50EA
When the UE Editor starts go into plugins and check the plugin is in the list
Update:- Since this question happened Quixel Support have found another problem which may not be directly related but the workaround was found. It is rather in depth but might help others
Quixel Bridge Failed to restart background service