Can't run Catalina 10.15.7. The computer just keeps restarting

Try booting up into macOS utilities. You can do so by holding command r. Then try restoring from time machine back up. If not, then if you have a lot of storage, then hold option command r. That’ll help install macOS Big Sur. If not, hold shift command r to install the most basic operating system your Mac can handle.

ferrisgw wrote:

HELP! I am tried in vain to run Catalina 10.15.7. The **** computer just keeps restarting, but does nothing else. I can't find any help on your website.

—The point update: Combo update macOS 10.15.7 https://support.apple.com/kb/DL2052?locale=en_US

or

—If the full installer is sitting in your Application folder "Install macOS Catalina.app"

Reboot into SafeBoot mode and try again.

Verify you have adequate free storage space to make this happen.

Try a SafeBoot https://support.apple.com/en-us/HT201262

Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc.

Login and launch your installer.