I use 802.11r together with wpa2/eap on 19.07.6, therefore I have to specify all this key stuff in the wireless config:
mobility_domain, pmk_r1_push, r1_key_holder, r0kh, r1kh...
This all is done somehow automatically if you use wpa2/psk and specify ft_psk_generate_local.
To my understanding the current AP knows the mac addresses of all involved APs (as they have to be all listed with r0kh and r1kh), and with the pmk_r1_push option every access point pushes all info needed for roaming in advance to all involved access points.
This is described here much better than I can do it:
https://blog.fem.tu-ilmenau.de/index.php?url=archives/1002-HowTo-enable-WiFi-roaming-with-hostapd-and-VLANs.html&serendipity[cview]=linear