It depends on your internal GPU. If it's an Intel GPU, you could use vfio-mdev, which allows you to split your physical GPU into smaller counterparts. It will only work with the macOS version that are compatible with Intel GPUs (probably most of them).

Have a look here for a guide on Archlinux : https://wiki.archlinux.org/title/Intel_GVT-g. And here for a script to deploy macOS on KVM : https://github.com/kholia/OSX-KVM.

Side-note : vfio-mdev can now be unlocked on consumer-grades Nvidia cards too : https://github.com/DualCoder/vgpu_unlock. Sadly, it is not possible for AMD-cards.

By the way, I am working on Phyllome OS (https://phyllo.me/), which is an attempt to make it easier to do such things. But please don't tell anyone :)