HTTPS Inspection is still a BETA feature.
I recently enabled it and tried it, but the functionality appears to be broken.
HTTPS Communication is not established even if HTTPS Inspection is bypassed.
According to support, to prevent the problem from spreading, the HTTPS Inspection documentation is being kept private.
[Related Topic]
MX HTTPS Inspection Coming ... - The Meraki Community
https://community.meraki.com/t5/Security-SD-WAN/MX-HTTPS-Inspection-Coming/m-p/45870