How to remove Mac OS Big Sur, I hate it.

Revert your Mac to a previous macOS version from Time Machine Backup

Or >>> the more involved method. The following will Wipe ALL DATA and there are not Do Overs - 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.

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. 

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.

See:

https://support.apple.com/guide/mac-help/revert-to-a-previous-macos-version-mh15216/10.15/mac/10.15

MtD

You have options. You can wait for Monterey which is due to drop very soon or you can revert to an older macOS release. Recommend nothing newer than Catalina. Apple typically only supports the current operating system minus two versions with security updates. Older than that is considered obsolete and unlikely to receive security updates. Once Monterey ships that means Catalina -> Big Sur -> Monterey will be supported. Mojave will be unlikely to receive updates. Anything older might start to lose support for newly updated Apps and iCloud, etc.

If reverting, you will need to backup your data with something other than Time Machine because Big Sur Time Machine backups won't be compatible with earlier macOS versions. Only applies if you had a Catalina Time Machine backup that you started backing up Big Sur after you upgraded then the drive would have been converted to Big Sur usage and you cannot restore to Catalina as a result. Carbon Copy Cloner / SuperDuper! or you could just copy your data files somewhere safe.

You will need to download the older operating system installer. The easiest way to do that is to open Terminal and type the following which would get you the latest Catalina installation.

softwareupdate --fetch-full-installer --full-installer-version 10.15.7

That will get you /Applications/Install macOS Catalina and you cannot run it within Big Sur but you can use it to create a bootable installer on a flash drive.

Then you will need to obtain a 16GB+ flash drive, format it as HFS+ and most importantly, name it 'MyVolume' and burn the installer to the flash drive via Terminal:

sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

Make sure your backup is in good condition. Then shutdown completely and hold the Option key while powering on. Choose the flash drive to boot. Erase the internal disk completely and then install Catalina to the internal disk. Install your applications and restore your data by copying it back into place.

If the computer came Originally with Big Sur installed - one can not downgrade to anything older that what it came installed with.