Website designer role

To borrow someone else’s words:
“You should not give administrator access to someone you would not give the keys to your house.
Administrator access means that I can change the contents of the wp-config.php file, change passwords” and all sorts of other things.

There is another way to do it.

You can use a role management plugin like this:
https://wordpress.org/plugins/advanced-access-manager/

You would then create a new role.

You would only assign that role the capabilities that they really need to do their job (the theme related ones, for the most part):
https://wordpress.org/support/article/roles-and-capabilities/#administrator