hmm, strange.
just tested 2 fresh win10 installs. both work fine....
1. ovmf, q35, spice (qxl)
installed win10 and no gvt-g device, added spice/qxl driver via virtio-win.xxx.iso
after install of win10, shutdown, add gvt-g device (minimal vX_4), keep SPICE enabled.
boot, install intel igpu...