No, Open Camera is a third party app by Mark Harman that you can download from the Play Store
and numerous other app stores. At least on the FP3 with the “old” camera modules many people have found it superior to the stock FPOS camera app, which is from Google (but not the Google Camera app which is officially exclusive to their Pixel devices).
I don’t think that app cache and / or data ist the main problem here. I just installed Open Camera yesterday on my Android 10 FP 3 and only made a few changes in the app settings so far. Nothing “special” though…
Thanks I gave it a go and got the same results as JeanChristophe. The image being stored is exactly the same and looks like a problem with the way it is being converted to save it. I tried changing the settings but none I tried including lowering the resolution to 8MP changed the result.