The GPU maker is locking certain functions on the Vega M platform that are otherwise commonly found on all other Vega GPUs including DirectX 12.1 support. In fact, the feature set of Vega M has more in common with the previous-generation Polaris platform rather than the current Vega family.
https://www.notebookcheck.net/AMD-Radeon-RX-Vega-M-is-a-Vega-GPU-without-some-common-Vega-features.296736.0.html