Installing Catalina (Downgrade Big Sur) No Back Up

I Need To Know How to Downgrade My MacPro to Catalina From Big Sure 11.1

I have Looked At Every Video And Followed Process But Have Not Gotten The Same Outcome .

I Have Tried To Make a Installer For Rebooting to Catalina But Get Stuck At ( Terminal ) With this Code

" The default interactive shell is now zsh.

To update your account to use zsh, please run `chsh -s /bin/zsh`.

For more details, please visit https://support.apple.com/kb/HT208050.

I Have typed In ( `chsh -s /bin/zsh` ) and hit enter and got This Code

chsh: no changes made

Every Video I Have Seen was Simple But My Terminal Wont accept the Codes .

Error When I add Installer link and USB that it needs To Install To

Please Help Big Sur Has Crashed My Music Studio From Cubase and Focusrite

Causing Audio Drop Outs Every Recording