Does Upgrading macOS Delete Everything?

No. Generally speaking, upgrading to a subsequent major release of macOS doesn’t erase/touch user data. Pre-installed apps and configurations too survive the upgrade. Upgrading macOS is a common practise and carried out by lot of users every year when a new major version is released.

Will installing new macOS delete my files?

Reinstalling macOS from the recovery menu does not erase your data. However, if there is a corruption issue, your data may be corrupted as well, its really hard to tell. … To gain access to the disk depends on what model Mac you have.

Will downloading macOS Catalina delete everything?

You can install Catalina over your current macOS, keeping all its data untouched. Or, you can get a fresh start with a clean install. The main benefit of clean installation is that you get rid of the system junk and leftovers which might hamper your Mac’s performance.