reboot with option key

lowellfrombrookfield wrote:

rebooting with option key isn't working. The MacBook Air just starts normally. Using Monterey. I want to reboot using an alternate MacOS drive with Catalina.

When the option key boot does not present another drive as a boot option, that usually means that the alternate boot drive is not a legitimate boot drive for that computer. For example, if the Mac came with an operating system later than Catalina, it won't be able to boot from a Catalina boot drive and won't show you that option at all. Or if the Catalina MacOS was not installed into the other drive in a way that made it bootable, you will get the same result.

What year and model is your Mac, and what process did you follow to create the Catalina boot drive?

Make sure you have connected the alternate boot drive and it is visible in Finder, then change the boot drive in System Preferences, followed by a normal restart.