Open Camera is really weird. Important that it is not a GrapheneOS app and thus not supported. I assume the GOS Camera and OpenCamera are fundamentally different and OpenCamera uses old Runtimes.
On my Nokia 7plus with LineageOS it was pretty good. Then on a more modern Pixel 4a it was unusable, even though newer Android version.
Then on my Pixel 7pro it was very fast, but that phone was a brick.
On the 6a it is slower but usable, 3s max delay on start, 2-3s delay on photo taking.