Disabling markdown at a section level is now supported in Cards. You can set markdown to false.
Details here
Example
{
"@type": "MessageCard",
"@context": "https://schema.org/extensions",
"summary": "Office 365 Notification",
"title": "Office 365 Service Degradations",
"sections": [
{
"markdown": false,
"facts": [
{
"name": "Service Incident:",
"value": "ID"
},
{
"name": "Start time:",
"value": "check_disk_critical"
},
{
"name": "Service:",
"value": "SERVICENAME"
},
{
"name": "Description:",
"value": "MESSAGE"
}
],
"title": "Office 365 Service Problem"
}
]
}