After the Volume Down Button fell out of the device, I'm wondering if there's a more reliable way to trigger the 3 Finger Screenshot Gesture? I find it to be as awkward as it sounds.
With OnePlus you have 3 options it looks like. Vol + Power, 3 finger gesture, and you can add a shortcut to your quick settings.
Quick settings method
Swipe down from the top of the screen to open the Quick Settings panel.
Look for the "Screenshot" button. You can customize the panel by tapping the three dots (⋮) or a pencil icon and dragging the screenshot icon to the active area.
My Samsung does not offer this 3 finger method for screenshots the way OnePlus does. I did find several videos on how to do the 3 finger gesture and while it doesn't look complicated to me perhaps seeing someone else do it may make it easier for you to see and mimic.