I don't have a Catalina Macbook. I have a Macbook Pro 17 which despite having 8G RAM, an i7, an SSD drive and a GPU will not upgrade past High Sierra
However I don't think that it matters whether you have bash or zsh. pscan won't care.
Please click into the xterm window that you have.
Please type these commands:-
cd /Applications/pscan.uk
./pscanloader
then tell me what happens