Currently, you cannot solely connect your calendar to HubSpot as it will automatically request access to the personal inbox. This means that HubSpot will obtain access to information that people and/or organizations are not willing to grant and therefor block functionality.
The option to connect and immediatly disconnect the inbox as now proposed in the documentation is not a solution with privacy-by-design in mind.
Because of this implementation we are now actively avoiding the use of the functionality as we do not want HubSpot the even temporary have access to the inbox of our users when integrated.
Creating seperate integration apps and therefor seperate permission requirements would allow users and organizations to make a better choice between what they want to share with HubSpot and also improve the security and privacy framework for those individuals and organizations but also help HubSpot be more compliant with GDPR regulations.