There’s a few bits of info out there mentioning Open Camera and RAW. Some are quite old but may shed light on what to look for.
How to shoot full-resolution photos in RAW on the Google Pixel | VentureBeat (An oldie from 2016).
This one is in French…
Prise en main d’Open Camera 1.35 : réglages manuels et format RAW - Les Numériques
Device support for camera2api is a must it seems.
There’s been some talk in the forums where RAW and cmera2api are mentioned like this one…
Picture quality, S7 - Using /e/OS / User Queries - /e/ community
Lastly, the Open Camera home may be the first place to look.