Unofficial is an understatement.
It might work but would probably require the Devils Canyon bios update to do so.
Even though both chipsets are LGA 1150, Broadwell was not intended to run on a Z87 platform.
If your looking at performance, hands down a 4970K would trounce a 5775C anyways, so I fail to see the benefit.
Intel i9 10850K@ 5.3GHz
ASUS ROG Strix Z490-E
Corsair H115i Pro XT
G.Skill TridentZ@ 3600MHz CL14 2x16GB
EVGA RTX 3090 Ti FWT3 Ultra
OS: WD Black SN850 1TB NVMe M.2
Storage: WD Blue SN550 2TB NVMe M.2
EVGA SuperNova 1200 P2
ASUS ROG Strix Helios GX601