But what if your not using ULib or making your own MOTD from scratch?
My fix above would be for the ULX MOTD only, but essentially the concept would be the same:
Take your existing MOTD code, find where it sends the URL to the specific player who will be shown the MOTD, then append the players SteamID to the URL (since you should have the player entity available).
If the MOTD code is clientside only, then you
should be able to append LocalPlayer():SteamID() to the URL, thus it will get the client's SteamID without going through serverside code.