@RebelMagpie
You can use this drive’r’s
[ST Edge] vEdge Creator: a virtual device generator for end users - Devices & Integrations / Community Created Device Types - SmartThings Community
temp/humidity device.
In setting is possible to select to dashboard humidity value.
Then you need Rules API rule that copies humidity measurement from real device to virtual device.
Here is link to Rules API rule that is copying Zigbee humidity measurement to virtual temp/humidity device.
Integration Solutions using MQTT - Devices & Integrations - SmartThings Community
Quite complicated but possible