The topic link (3rd point) was the way to go, thanks !
I ended up using a signed distance field and clamping my plane according to the distance field’s value, which allowed me to render only the cross section.
However, if anyone comes across this in the future, I think it’s worth mentioning that mesh distance fields have been disabled on Intel graphics cards.
“All Mesh Distance Field features have been disabled on Intel cards because the HD 4000 hangs in the RHICreateTexture3D call to allocate the large atlas.”
source (hardware limitations): https://docs.unrealengine.com/5.0/en-US/mesh-distance-fields-in-unreal-engine/