Clean Install of Big Sur on iMac 21.5

BACKUP YOUR DATA BEFORE PROCEEDING!

Control has nothing to do with it.

You will need a wired keyboard to issue startup commands. Apple's wireless keyboard usually has a lightning port, which you can link with an iPhone lightning cable to the USB port of the Mac. Not all do, but many do. Any Windows keyboard that is USB that does not require specific drivers should work. I have run into a couple keyboards sold at K-Mart that don't work at all.

Alt/Option key will get you the startup manager.

The system restore is Command-R for the existing system. If you are careful with Disk Utility you can wipe the data partition and reinstall the operating system presently on the system

command-option-shift-R at startup will let you restore original system that shipped with your Mac, as long as you have wiped the entire hard drive, and have a hard wire or secure WiFi connection to the internet.

Note, "clean install" has at various times meant different things, and we are assuming you want to completely wipe your system and start with nothing but the operating system.

A simple USB mouse can be purchased for $10-$20 at an office supply store.

Most don't require special drivers for Mac OS X.

If you can borrow a cabled mouse for a short time( if it’s from someone who works with a windows PC, that.s ok) you can proceed further without installing drivers