It's not been made immediately clear - in Germany (where Sky have their HBO deal) it's showing on WB'S TNT Serie Channel - it's also going to TNT in Spain who have a HBO D2C service! But then one or two tv sites stated it was a co-production with Sky Studios though it's never been confirmed by Sky themselves so I have doubts about that. It was also originally produced by WB for the US TNT Channel so it could be that it does not fall into the Sky output deal.
If Sky did have the UK rights I could easily see them holding it back - for a box set release, to have some content for 2021 and to keep it out of the way of their own Brave New World which comes in the next couple of months.
I find so very little that interests me in the Now TV entertainment section, however I've been buying 2 month passes for £10 for the past year or two and have been tempted buy their reduced fees when cancelling, to date it's been quite cheap even though the PQ and sound is poor it's been just about worth it. Now I see that those cards are no longer available but have been replaced with 1 month cards for £8.00 (a 60% increase!) and still at low PQ and stereo sound. I can no longer justify the expense, especially in competition with Amazon Prime and Netflix. I shan't be renewing next time.