Looks like you might have deleted the module role User in MyFirstModule, but it is still assigned to either a microflow, page or application wide user role.
Double clicking the error will usually point you towards the Microflow of Page with the issue. In this case, you can re-select the user roles under allowed roles in the properties window.
Lastly, you can check the security tab under under project in the project explorer. You might have a user role that is assigned to the User module role from MyFirstModule, which has been deleted. In that case, you might need to re-select the roles there.
Easiest fix would probably be to re-create the User module role in MyFirstModule -> Security. Was there a reason you wanted to delete it?
Have a look at this for more information:
It seems you removed the user role User from your MyFirstModule. You can have user roles defined on the project level and on the module level. Open the security in MyFirstModule and add the role again or in the project security change what module role a project role has. So let's say you have on project level admin, manager and user. On the module level you have admin and user. Then on the project level you can set which role a role on project levels has on module level. So a manager on project level can either have the user or the admin role on module level.
See also this learning path: https://gettingstarted.mendixcloud.com/link/module/96/lecture/788