I see people saying this a lot but Sony hasn't had a big 1P release for PS5 so far this year and they're breaking sales records.
It's not JUST lack of 1P games why Xbox sales have been slowing down heavily. It's a multitude of factors: lack of perceived value in Game Pass, Day 1 of all 1P games on PC making buying a console increasingly redundant, lack of marketing rights to big 3P AAA releases, lack of marketing for the console by Microsoft in the traditional advertising spaces, bad messaging, general dilution of brand perception over the past 13 years among various gamers, bad pricing, etc.
People want to simplify the problem to just lack of 1P games and lack of Series X units, but it's not.