2 weeks ago, I did the system update to install Big Sur on my work laptop. Running Selenium tests in Chrome was really slow and tests failed all the time.
It took about 4 mins to login
to our portal. Very Slow. When using Safari to hit our portal, I got the same
result.
Since this is the work laptop,
I decided to downgrade from macOS Big Sur to Catalina. I watched many YouTube
videos. This video
is pretty good.
I followed the instruction,
but I got the following screenshot.
Security settings do
not allow this Mac to use an external startup disk
After looking into the issue,
it was easy to fix it.
Went to Utilities ->
Startup Security Utility. Logged into my credential.
Changed to Medium Security and
chose Allow booting from external or removable media.