I have noticed that even when changing to native resolution with 200% rendering resolution the game still looks really pixelated.
The fix I found for it is to go to the game config file and manually change the resolution.
Pixelated resolution FIX
1. Press WINDOWS key + R
2. Type: %appdata%
3. Then go to the folder: SEGA\P5R\Steam\*YOUR_ID*\
4. Right click ScreenSetting.xml then left click edit
5. Change those values to your desired resolution:
width="2560" height="1440" resolution_width="2560" resolution_height="1440"
6. Press Ctrl + S to save and close the text window
7. Launch the game and enjoy!