When connected to external display in clamshell mode, some people have had success using SwitchResX to find a resolution that keeps dGPU wattage down. (External display forces dGPU, and high dGPU wattage even at idle seems to be causing high temps/fans. See the epic macrumors thread.)
If not connected to external, there are ways to force iGPU (e.g. sudo switch - details also in that thread). Not sure if Cubase itself requests dGPU, but some third-party plug-ins do. May help in this case.
Or now there is the revoltingly expensive 5600m graphics option (€1,000 over base model), which seems from initial reports to be quieter with external display and under dGPU load, also slightly higher CPU benchmarks.
Still on the fence here - would appreciate any experience with Cubase using these workarounds.