LOOP TOOLS ADD ON

Have you switched on the “Allow Online Access” function under Preferences -> System? Otherwise have a look at “Get Extensions” (see pictures)
I have not yet fully understood the new structure, but I also had the problem that the “Allow Online Access” function had to be activated and this was displayed under “Get Extensions”.

And if you have activated the function, you have to go to “Get Extensions” and click on the Install button again. However, it will then also be listed under Addons