I have some R7800 APs and read in the forum that beamforming has not to be activated manually. But for Belkin RT3200 (https://openwrt.org/toh/linksys/e8450) there is a not on the device page that it should be activated by:
Checked hostapd-phy0.conf and hostapd-phy1.conf under /tmp/run and also the logfiles but there is no beamforming entry for Netgear R7800 and Zyxel NBG6817 but for Zyxel WAX206 if the settings are added...does this mean beamforming is inactive for R7800 and NBG6817 even if it has a supported flag?
Found a thread that pointing out beamforming is active for Wifi5 by default and for Wifi6 is not. That should be the case because both devices behave differently.
This is the reason it should be enabled manually for Wifi6 (AX).
To my knowledge BSS color has no special meaning related to beamforming. And certainly there is no magic value 8.
(BSS color is just a (pertty much randomly selected) ID used in wifi6 to indicate which BSSs are related in a "multiple APs overlapping" situation.)
This ''''Solution''' seems to be a mis-interpretation of the (generation of the) actual phy configuration (or inappropriately generalizing the finding on some of the OP's devices). It is of note that the ieee80211ax flag is missing in the OP's phy config of the ' Zyxel NBG6817/also R7800' devices...
For another Wifi6 device (DAP-X1860), the beamforming is active immediately upon factory firmware flash of OpenWrt 23.05.2, r23630-842932a63d.