In the following use case the transition will only be displayed, if the current user is in project role Administrators.
Add the condition to the desired transition or create a new transition.
Choose Current issue
Choose All users are at least in one of the selected project roles
Choose Administrators
Select the project roles according to your needs.
Enter the following message in basic text mode:
You need to be in project role "Administrators" in order to execute this transition.
Users are/aren't in project role (validator)
Users are/aren't in project role (condition)