Hi @NikSchet,
An update here: we’ve recently focused on allowing backpropagation support for default.mixed and enhanced compatibility with JAX’s vmap.
See the following (approved) pull request that will be merged into master and is to be released with v0.25.0 of PennyLane: https://github.com/PennyLaneAI/pennylane/pull/2776
Furthermore, we also have GPU support for default.mixed with Torch on the radar.