Thanks Tony,
Here is the relevant section of the logs:
Host OS: Version 12.4 (Build 21F79)
Metal Device: AMD Radeon Pro 560X (lowPower:NO removable:NO headless:NO unifiedMemory:NO location:MTLDeviceLocationBuiltIn gpuFamily:MTLGPUFamilyMac2)
API: Metal
GPU: AMD Radeon Pro 560X
Which tells me the Radeon is active. But when I use Activity Monitor to see what cards are being used the Radeon isn't active.
I also have Train Simulator 22 running under Crossover which has better graphic performance than Trainz, and Activity Monitor is showing the Radeon is active.
So still puzzled.
Andrew