We do plan on adding support for guest users to submit approvals.
18 months.... we are waiting for this feature. Thanks.
It's note THE expected answer, but I'm using this workaround for months now: I used my "assigned to" user also in the "requestor" field.It's not so clean because you can't see weel in the request list who made the request, but it works!
This is a huge win for Microsoft Flow if they can pull it off!
Waiting for this too
Just started woking on Approval flow (because for Dynamics 365 VOC deprecation) - can't believe we cannot use an extenal non-office 365 email address already ... looking forward to the feature