It depends on the app, not GOS.

I'd check if Aves works (gallary): https://github.com/deckerst/aves (in Accrescent)

And for editing: https://f-droid.org/packages/ru.tech.imageresizershrinker/

I don't think it's an inherent limitation of GrapheneOS, and more just a limitation of the default photo app. What did you use to edit raw photos before?