I normally see this every time I switch branches with this version of Xcode (13.1). If I delete the derived data folder contents sometimes it will reindex correctly other times I have to do that and then reboot the machine. It has been horribly inconsistent. I can see hundreds of errors but yet it will build and run on the phone. This really needs to get fixed, as you state above it causes a ton of usability issues. I hope it works better for you, not sure what is going on maybe if you aren't running one of the M variants Xcode just isn't happy any longer. Or maybe no one in Apple tests with complex large projects combining Obj-C and Swift either way it is happening not only on my machine where I work but the other iOS developer is seeing the same thing. Note: I do not switch branches inside of Xcode maybe that would help it realize what is going on.