Swiping from either the left or the right of the screen within the app (not the navigation bar) is the Back gesture. Apps are supposed to avoid implementing conflicting gestures, but have the option to override this gesture if they truly need to get rid of it. Some legacy apps without active development of their UI still haven't addressed this despite gestures being the default for several years on Google Android. You can avoid triggering the back gesture in one of 2 easy ways: avoid swiping from right near the edge or hold your finger on the side of the screen for a moment before swiping. The more advanced option is using a diagonal swipe pointing sharply to the bottom of the screen since this will bypass the back gesture but will still trigger most app gestures. The advanced option is the most convenient approach once you get used to doing it.
Unlikely that GrapheneOS would implement something like this, unfortunately. It's mostly apps that have to keep this in mind and develop/design their apps accordingly. I understand it might not help you in this case, but it is what is is. :/