I updated Visual Studio 2022 Pro this morning to version 17.2.6
When it finished updating, I opened my project and nearly every line of any file I opened suddenly had errors for things like not recognizing strings as System.String or void as System.Void. At one point it was showing 24,000 errors with only 1 file open.
I tried repairing visual studio, restarting my computer, modifying the program with anything that seemed helpful, but nothing fixed it.
Importantly, whenever I built the solution, all the projects would succeed and it could run.
Remove .vs folder or just .suo file in .vs\<solution_name>\v17 folder.