Why does Visual Studio 2019 doesn't show the list of next possible codes and doesn't show in green variables like Sprite or Image?

I recently moved my project from Unity 2018 to Unity 2019, and now Visual Studio 2019 doesn't recognize some specific variables (like Sprite or Image, but does recognize int, bool, etc) and other classes.

Despite the codes still work, they all show in white (instead of green) and the automatic code propositions don't show up after a ".". Another example is that I can't even write "gameObject" so that it recognizes what possibilities there are after that. Hovering over theses variables doesn't show any information... Visual Studio also used to keep all my scripts open when I close it and come back to it, but now it's not the case anymore. I have to reopen all scripts I want to edit.

I'am not so competent with Visual Studio, so easy words plz! :)

Does someone has any idea of why and how to repair that?