When using the "Send an email from a shared mailbox" trigger in Flow, FullAccess permissions are required in order for the flow to succeed. Please fix this because giving that amount of permission to a mailbox should not need to be required to send an email as a shared mailbox. I created ticket REG:118030917787218 with Microsoft and the tech said they can't fix the issue because it is working as designed and referred me to post the complaint here.