> Getting an update to stick
I can’t update my Mac from Catalina 10.15.6 to 10.15.7. Each time I update and restart, it’s stuck with the old version. How can I get the update to work?
Ensure you haven’t modified your System, for example by disabling SIP. If you can’t get Software Update to work, try a standalone installer from bit.ly/mac360downlo. If necessary, download and run the Combo updater. If none of those methods work, you may need to perform a clean reinstall. Make at least one complete backup and ensure that all your important files have been saved to it, then restart your Mac with the Opt+ Cmd+R keys held down on a wired keyboard, or from a bootable external copy of macOS 10.15.7. Open Disk Utility, select your startup System volume, by default named Macintosh HD, and click on the Erase tool. Format it in APFS with a GUID Partition Map, and enter your Apple ID if prompted.
Once the volume has been erased, install macOS. You may then be presented with a choice of volumes on which to install it: pick the newly formatted System volume named Macintosh HD. With a bit of luck, your Mac will end up with macOS 10.15.7 installed and connected to its original Data volume, which won’t need any further restoration.