How do I downgrade my Mac from Big Sur to Catalina?

How do I downgrade my Mac from Big Sur to Catalina?
Downgrade Big Sur using Time Machine

Erase your Mac’s system disk.
Restoring your Mac using Time Machine.
Create a bootable drive for Catalina.
Prepare your Mac to boot from USB.
Installing Catalina from USB.

Downgrade Big Sur using Time Machine
  1. Erase your Mac’s system disk.
  2. Restoring your Mac using Time Machine.
  3. Create a bootable drive for Catalina.
  4. Prepare your Mac to boot from USB.
  5. Installing Catalina from USB.
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