The King has been overthrown. Call of Duty games have debuted at #1 on the sales charts in the UK every launch week since I believe CoD 4 in 2007. However, this was not the case this year, Assassin's Creed Valhalla lead Call of Duty on the UK physical charts for the week, according to a gameindustry.biz writer:
For the first time in about 80 years, Call of Duty is not No.1 in the UK physical charts during the week it came out... in a major week for game sales, Assassin’s Creed is the biggest boxed game— Christopher Dring (@Chris_Dring) November 15, 2020
Worth noting that this is the physical chart only, Call of Duty may have lead on physical + digital combined in the UK, though that is not certain, since Ubisoft has reported increased digital ratio for all of their recent Assassin's Creed games, with Origins in 2017 having a physical/digital ratio of 65/35, Odyssey in 2018 with 55/45, an increase of 10% for the digital ratio in just 1 year; 2 more years have passed since 2018, so AC Valhalla could be well over 50% digital now.
Edit: Some further updates from him:
Call of Duty Black Ops Cold War sold 65% fewer copies in a box at launch than last year's Modern Warfare (UK figures). However, Activision says the game broke franchise records in terms of day one digital sales... so it's difficult to know how well it did or didn't do— Christopher Dring (@Chris_Dring) November 15, 2020
So, numbers time. In the UK, boxed sales of Assassin's Creed Valhalla are double what Assassin's Creed Odyssey managed— Christopher Dring (@Chris_Dring) November 15, 2020