I think you need an MSFS equivalent of the P3D’s PDK Rendering System, which I don’t think is available. With the PDK’s rendering system, textures could be created and referenced elsewhere.
This is an example on P3Ds website of creating a texture.
https://www.prepar3d.com/SDKv4/sdk/pdk_api/samples/texture_and_effect_render_plugin_sample/dll_main.html
I believe this is what @Umberto67 uses for the fuel display (Render To Texture - RTT) for the fuel trucks in GSX. @Umberto67 , do you know if the equivalent can be done in MSFS2020?
Kind Regards
Craig