Wouldn't Demon Souls Remake, Ratchet & Clank, & Returnal naturally cater to JP gamers as far as 1st party titles go?
I'd like to see them build more internal JP teams too similar to what they had with Japan studio but they do get a lot of JP support and have various dealings to get games like Granblue Fantasy Relink, Final Fantasy 7 Remake/FF 16, Genshin Impact, & investing in the China Hero Project.
If you want to know what is (currently) most successful in the PlayStation space in Japan, one only need look at the data, but ignoring the PS4 era for a moment, here are the Top 5 best-selling games on PS4/PS5 since the launch of the PS5 in 2020:
Tales of Arise - 273.580
Biohazard: Village [Resident Evil: Village] - 264.744
Call of Duty: Black Ops Cold War - 188.413
Lost Judgment: Sabakarezaru Kioku - 187.623
Kimetsu no Yaiba: The Hinokami Chronicles - 161.344
As for the three you mentioned:
Demon's Souls Remake - 58.661
Ratchet & Clank: Parallel Trouble [Ratchet & Clank: Rift Apart] - 24.385
Returnal - 14.749
Returnal specifically is the 3rd worst-selling SIE game in the PS5 era thus far, behind only Sackboy and Destruction All-Stars. The best-selling is Marvel's Spider-Man: Miles Morales at 104.675, though as you can see by the Top 5 even this isn't especially remarkable, and is no doubt helped by having a PS4 SKU (whereas the other 3 do not). Among the Top 15 best-sellers on PlayStation in the same period, only 1 game is first-party (the aforementioned Spider-Man).
Looking at only the PS5 SKU, Demon's Souls Remake is just behind Miles Morales, but it's a far cry from Bloodborne or Dark Souls III.