The Mendix portal for SAP BTP deployments lacks control on the order of environments.
Once an environment is added there it will forever stay in the creation order.
When creating multiple environments, or changing environments, or removing them, you end up with an arbitrary order.
If by chance a PROD environment ends up on top, this is always auto selected for the first deployment.
If you select Transport from another environment you will also end up with an arbitrary selection.
It should be possible to change the order of environments in the portal and also to define the Default for Transports such that it is possible to configure a proper TEST → ACCP → PROD pipeline on an existing application.
I can definitely support this idea. Especially for applications used across different business units at our company, you get a complete mess in the environment overview, when environments are created at different points in time (TEST for BU 1, then PROD, then TEST for BU 2, etc.).