2019 iMac cannot upgrade macOS Sequoia 15.7.1 to 15.7.3

To update, follow the instructions at > Update macOS on Mac - Apple Support

If you are running any third-party Anti-virus, Cleaning, Protection software or a VPN, disable or preferable uninstall those from your iMac and then try updating.

Backup your data before doing any update or upgrade.

https://freemacsoft.net/appcleaner/

offers an excellent application uninstaller that removes all

dependencies of an application. Sometimes you have to login as safe

mode (holding the shift key) to be able to use it.