You cannot run or compile 32 bit applications on Catalina or later because 32 bit support has (mostly - there are some Carbon bits left) been removed. Mac computers have been 64 bit capable since 2007.
This:
CarbonBars.pas:
{$IFNDEF cpui386}
{$ERROR only cpu i386 is supported}
{$ENDIF}
suggests that you are trying to compile for 32 bit (i386) instead of 64 bit (x86_64).
Go to Project > Project Options > Compiler Options > Config and Target and setup as follows:
Target OS: Darwin
Target CPU Family: x86_64
Target Processor (Default)
Current LCL widgetset: "Cocoa"
Cocoa is 64 bit; Carbon is 32 bit.