Visual studio 2019's intellisense not working with Unity 2020.1 & 2020.2

Visual Studio's IntelliSense suddenly stopped recognizing unity's classes and stuff while I was editing my scripts. I've been investigated these last couple days and I've acknowledged that what's probably causing this is that this box has in it "Miscellaneous files" instead of something like "GPU instancing" To fix this, I've tried a lot of things, I put Visual Studio in the "external script editor" box in unity both normally and browsing, I've reinstalled Unity and Visual Studio, reimported assets... but there's one thing I didn't manage to do (the most probable solution); "attach" VS and Unity through VS, the problem is that the button that did this action, called something like "unity connectivity" and located on the bottom left, has disappeared in the latest versions of VS, probably because the way of doing this has changed, and I can't find this new way of doing this action. How can I fix this? Thank you for reading