It was a lot of work, but we had enough staff to make it someones job for half a year or a quarter, depending on how bad the migration is. With big codebases there are other issues that pop up with every new major Xcode release that we have to migrate, mitigate or fix. For example we are still at xcode 11 because of various bugs in xcode 12. Doing the migration was annoying, but it was not much compared to all the other issues, because the fixes were tractable.