I understand what you are seeing. There are several issues that cause this to happen. I’ll start at the top:
The spinning + icon comes as a result of adding an album that you already have in your library. There are a couple of reasons why Roon sets you up for this, which I’ll get too. But if the album is there, and you click +, it will spin.
The + icon is sort of stupid. It will let you click it under some circumstances even if the album is there (I’ll get to that next). Once you know about this interesting ‘feature’ notice that if you click the three dots just to the right of it, the ‘Add to Library’ text is greyed out. IT knows the album is added, but the + icon doesn’t. So you click it, and it spins. Almost forever.
One reason why the + icon is there even though the album is already there is that it does not refresh automatically in some circumstances. In your screen capture you are hitting the back arrow, which brings up the same screen you were in before, and the + icon hadn’t refreshed. So you click on it again (and the album is actually already there), and it spins.
There are other reasons the + icon will be there even if you have the album, but that has to do with the Versions feature not showing what is or isn’t in your library properly.
How do you make it stop? Well, if you go to the home screen and go to Recently Added you’ll see that album there. If you click on that album you just added it will take you to the album page and refresh the page. Now the heart icon is there.
What can you do to avoid this? One is to know about these features and not fall for some of the traps. But I’ve found that I should not rely on the + icon. I click the three dots and Add to Library. Then you can heart individual tracks.
Simple.