Thank UK regulations for that, even after the mobile networks are ready the updates for all smartphones have to be cleared by the mobile signal regulators for safety reasons. They take an age perhaps because there aren't enough people working in their offices. Either way, expect it to be a month or two behind the rest of the world
I'm waiting for the update in Spain, I have the SM-T865 (Galaxy Tab S6 LTE version). I could saw that the update is running in another countries like Germany so I'm still trying the manual update search every day.