Can I boot from the built in SSD

Hello everyone,

Boot time for my mac 2017 is around 5 mins after a rather messy upgrade to Big Sur.

I notice I've still got the now redundant OS Catalina on my SSD - see image below.

The start up target drive is the Mac HD - where Big Sur is stored.

Is it OK to erase the SSD, copy Big Sur across to the SSD, and then make my SSD the start up target?

And if that is OK, can you point me to a talk through on how to do that?

Thank you.