Rollup helper flow fail: INSUFFICIENT_ACCESS_ON_CROSS_REFERENCE_ENTITY: Access to entity 'AggregateResult' denied: Entity is not api accessible.
This issue is likely coming from still using the default running user for Rollup Helper, you should be able to avoid this issue by updating the running user to be an actual user from your environment.
To change the running user first go to Scheduled Jobs from setup and delete the old Rollup Batch Agent - Hourly. Then go to the all Rollups page and click the gear icon button, in the top right of the screen, then click the change running user button.
The bottom left of the screen should then be updated to say the rollups are running as the logged in user, and the Rollup Batch Agent Hourly will be recreated on the scheduled jobs page.
that is correct the issue is likely due to the running user for Rollup Helper and that is how you can update it to be a user from your org with the correct permissions.