If you compare Demon Slayer and Jujutsu manga sales trends after their anime finished, you will notice they aren't even close, DS kept increasing and selling 1M+ each week for over year while JJK just kept decreasing even its last volume decreased from the previous one ( and apparently its Collab with Daido coffee which was huge success with DS, didn't actually work that well)
Here is the sales for the manga volume that was released before the movie for each of them after 4 weeks
Jujutsu Kaisen #17
1,520,532
Demon Slayer #21
1,837,089
Demon Slayer Special Edition #21
1,198,180
I would compare their volume 1 but JJK 1 isn't charting anymore.
So dunno but I feel JJK will make about 10B total with 15B being possible but not seeing bigger than that.