Downgrade from Big Sur os

The computer can only be downgraded to the version of macOS it came with as New and nothing lower.

A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS. 

Or and the involved method Scorched Earth Method 

This method will WIPE ALL Data and there is No Recovery - Period.

To perform this action will require booting from a Bootable Installer. 

This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer. Example : Bootable Installer of Big Sur would have to be done on a computer that Qualifies to run Big Sur.

Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can not be used.

Once that is done read on for preparing the Destination computer  >> Only works on Intel Based Apple Computers.

Extra Special Notation regarding the Touch ID equipped Apple Computer.

About Startup Security Utility and Must Enable from Recovery Mode the ability to boot from External Drive Before Attempting 

1 - Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

2- Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive. 

3 - It will present options >> Disk Utilities >> View >> View ALL attached Drives. 

4 - Choose the Upper Most Drive ( not the volumes indented and list below ).

5 - The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map. This applies to macOS 10.14 Mojave and above. 

5A - Formatting for macOS 10.13 High Sierra and below requires HFS Journaled with the GUID Partition Map

6 - Once that is done >> backup out of Disk Utilities and choose install macOS. 

7 - Follow the prompts and it may automatically reboot several time. 

8 - Upon a final reboot - Setup Assist will present with the newer version of macOS.

A downgrade is a substantial PITA, and if you had stated the specific printer make and full model identity, we might still be able to make it work if either Big Sur drivers are found, or the printer is supported by Apple's built-in AirPrint.

Waiting only 4 minutes after your original post to submit a separate related post is not providing anyone sufficient time to respond.

Related ?

Printer won’t work with Big Sur - Apple Community

Would tend to explore the previous advise vs the Scorched Earth method.