Currently users who have apps shared to them from a non-default environment cannot navigate to access the app from the powerapps website unless they have 'environment maker' roles. Assigning this role will then allow users to navigate to the non-default environment and open the shared app. However, I do not wish to provide maker access to users, I simply want them to have access to the app only. As it stands, if people do not have this role assigned they are not able to access the non-default environment from the drop-down menu.
Please consider providing access to shared app in such cases via the browswer as users are able to access the apps via mobile devices with no such issue.