Hi Björn,
It sounds like the Mendix application side is already resolving correctly to the private IP, so I would focus on DNS resolution from the Grafana environment.
A few things I would check:
nslookup <your-app>.azure.mendixapps.io or dig <your-app>.azure.mendixapps.io and verify which DNS server is being used.azure.mendixapps.io Private DNS zone is accessible from the VNet/subnet where Grafana is running.168.63.129.16), a custom DNS server, or another DNS resolver. The resolution path can be different depending on this configuration.Since the Mendix application itself resolves to the private IP but Grafana resolves to the public IP, comparing the output of nslookup/dig from both environments would be very useful.
The Private Link configuration is also worth checking, but I would first establish exactly which DNS resolver Grafana is querying and whether that resolver has visibility of the azure.mendixapps.io Private DNS zone.
If you can share the nslookup/dig output from the Grafana environment (with any sensitive information removed), it should be easier to narrow this down.
Kindly mark this as the accepted answer if it helps.