Hi Partner,
There is no need to change anything in the last step "Connect the record to the incoming activity".
I just change table in the 'Create a record (don't rename this step)' step without any other changes, then all run OK.

The 'PrimaryEntityReference' can be populated with value from last step automatically.


So you need check the following things:
1.Enable 'Creating a new activity' for the custom entity,
Activities (like emails or appointments) link to reference data through their regarding lookup.?
-----Power apps page:
-----Classic page
----current entity will build relationships with activity entities(include email) automatically if it has been enabled.

2.Add the custom entity to current app.
3.Check 'Regarding' field of the email:
--Make sure that custom entity as one type of the regarding field in email:

--Only the regarding value of the email is the custom entity record, you can view it in the timeline of the custom entity:
