Decided to do some digging and see if I could come up with all of the launch window (Q4 2020) games for both PS5 and Xbox Series. Here is what I have found. Let me know if I am missing anything.

Key

FE- Full Exclusive

C- Console exclusive

T- Timed exclusive

TC- Timed console exclusive

TN- Timed next-gen exclusive

F- Free graphical update

P- Paid remaster/port

Games that are on both systems launch Holiday

3rd party multiplat new releases

• Assassin's Creed Valhalla
• Bridge Constructor: The Walking Dead
• Call of Duty Black Ops: Cold War
• Chivalry 2
• Haven
• Lost at Sea
• Outriders
• Override 2: Super Mech League
• Planet Coaster
• Poker Club
• Puyo Puyo Tetris 2
• Recompile

Graphical Updates/Remasters for Games that release before the new consoles

• Marvel's Avengers | F
• Control | P
• Dead By Daylight | F
• Destiny 2 | F
• Devil May Cry 5: Special Edition | P
• Dirt 5 | F
• FIFA 21 | F
• Fortnite | F
• Madden NFL 21 | F
• NBA 2K21 | P
• Observer: System Redux | P
• Rainbow Six Siege | F
• Watch Dogs: Legion | F
• WRC 9 | F

Playstation 5

Exclusives

• Astro's Playroom | FE
• Bugsnax | TC
• Demon's Souls Remake | FE
• Destruction All-Stars | FE
• Godfall | TC
• The Pathless | TC
• Sackboy: A Big Adventure | FE
• Spider-Man: Miles Morales | FE
• Vigor | TN
• Worms Rumble | C

Xbox Series

Exclusives

• 12 Minutes | TC
• The Artful Escape | TC
• The Ascent | C
• Bright Memory | C
• CrossFireX | TC
• The Falconeer | C
• Gears Tactics | C
• The Medium | TC
• Tetris Effect Connected | TC
• Yakuza 7 | TN

Graphical Updates for Older Games

• Forza Horizon 4 | F
• Gears 5 | F
• Ori and the Will of the Wisps | F
• The Outer Worlds | F
• Sea of Thieves | F

Worth noting that my list seems to be missing alot, at least for Xbox. Microsoft claims they'll have over 50 games available this year on Series X that are either new releases or graphical updates for older games, but I could only find 33 of those 50+ games so far.

In the Key, maybe FR for the free graphic update? There are 2 F's.

Demon's souls

was rated in Korea in august 13.

there is a real chance of being launch/ launch window

I don't think there is a release date yet for that one.

Changed Full Exclusive to FE on the key to prevent confusion. 

Demon's Souls remake was announced without a date or window, Most likely a 2021 release, not launch window.

Edit: Hmmm, I see where the game just got rated in Korea, which has prompted speculation that it will be a launch window title. I will leave it off the list for now until we get an official announce from Sony. 

rated august 13 in Korea

Demon's Souls has been rated in Korea and Japan, and based on the history of timings between ratings and launch, Demon's Souls could very well be a launch title. Or launch-window. I'm not saying "add that to the list" (which looks accurate to me), but I'm sure that will interest people who check out this thread.

Edit: Apparently I take too long to type since everyone has pointed this out already XD

Man I hope so.  

Since when is Yakuza 7 a timed next gen exclusive for XSX? o.O