802.11k is supported for Raspberry Pi 4B/2GB.
Please see below response from Digi-Key engineer:
“802.11k was an amendment that was first included with 802.11n
For the RPI4, it’ll still need to be controlled by hostapd or other AP software to enable it… It also relies on the brcmfmac linux driver supporting the feature (while in ap mode)…”
Summary
1690-RaspberryPi4B/2GB-ND
RASPBERRY PI 4 MODEL B 2GB SDRAM
ARM® Cortex®-A72
5A992C SC
8471.50.0150
1690-RASPBERRYPI4B/2GB
1874652
71755296
SC0193