this is not how FT works, you should not see any new DHCP request at all. purpose of FT is that client seamlessly (at least much faster) connects from ap1 to ap2, keeping ip address, network up with really minimal service disruption. basically you should not experience any network hiccups (maybe some).
But FT must be supported by your clients foremost, they initiate the roaming by default. If your client is sending DHCP request because lost its IP address, then most probably your client does not support FT roaming and/or incompatible with your AP settings (e.g WPA3 and FT may not work very well).
Also you are referring to a 6years old post, i suggest to search in this forum or wiki first if you are using openwrt for up to date content.
as OP did not specify much detail regarding his/her setup it is hard to judge if that post is relevant or not. on its own it is on 19.x very likely, as i also learned from it at the time. but on 21.x it is automagically works out of box without the need to set any mobility domain and co (if every client and ap supports FT but it's not owrt to blame if not).