How to switch off "Not RRM Network" messages

My system's logs are being swamped by these messages:

wpa_supplicant[390]: RRM: Ignoring radio measurement request: Not RRM network

I have searched extensively; I've even found the sources for wpa_supplicant here: git clone git://w1.fi/hostap.git
But I'm not fluent in C and have no clue how to proceed. Can anybody suggest how I can suppress or avoid these messages or switch off this functionality?

EDIT: This is on Raspbian (Debian flavor for Raspberry Pi) Buster, which has wpa_supplicant v2.8-devel. It is communicating with a Fritz!Box AP; I mention this because I'm getting the feeling that could be relevant.

EDIT(2): as requested:

$ ps -f -p $(pgrep wpa_supplicant)
UID        PID  PPID  C STIME TTY      STAT   TIME CMD
root       342     1  0 Jul12 ?        Ss     0:02 /sbin/wpa_supplicant -u -s -O /run/wpa_supplicant
root       386     1  0 Jul12 ?        Ss     0:04 /sbin/wpa_supplicant -s -B -P /run/wpa_supplicant.wlan0.pid -i wlan0 -D nl80211,wext -c /etc/wpa_supplicant/wpa_supplicant.conf -C /run/wpa_supplicant