You could try going to the Power Apps portal page > Data > Connections and then find the connection and click on the three dots > switch accounts and see if that works.
For some reason the user does not have access to this section even after we have shared the app with him.
In fact he doesn't even have access to the environment.
Also looking for this solution, interested to know if it is possible to achieve this with e.g. Edit Connector Role Assignment ref: Power Apps for Makers - Connectors | Microsoft Docs
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