I've personally not used MacOS Catalina. It may or may not require you to run
chsh altogether as the superuser (i.e.
chsh -l (lowercase L) to see a list of the shells available to you.
As changing a user's shell modifies
/etc/passwd, you'll only be able to modify your own user's shell if you don't run
sudo or as the
chsh interactively (i.e. Without any arguments) should then prompt you for the pathname to the shell you'd like to set as your default shell.
Additional arguments that you could use include
--list-shells which displays the list of available shells located in
/etc/shells. This is useful to see the full pathname of the available shells that are accepted when designating a default shell with
chsh. This could be very useful in
-s shell /
--shell shell , where shell is the path to the shell you wish to designate as your default shell.