Errors Everywhere when updating unity

So I just updated my project for the first time from 2020.1.6f1 to 2020.1.8f1 and omg when I opened Visual studio I had a heart attack, haha. Most of the errors have “The type of namespace name could not be found” error and “The name does not exist in the current context.” My code was completely ok before this, I have no experience in updating unity and I’m wonder two things, 1. How do I fix these errors? 2. Does these happen every time you update? Thanks168963-capture.jpg

In Unity, go to Edit < Preferences < External Tools ,
change external script editor to visual studio 2019
I usually have this problem when I do a new update.