Quick answer: Godot 4 Camera2D with smoothing enabled jittering more than without? Smoothing runs in _process while target moves in _physics_process - interpolation gap causes the jitter.
Player follows via Camera2D smoothing. Movement at 60fps stutters visibly.
Enable physics interpolation
Project Settings > Physics > Common > Physics Interpolation. Engine interpolates between physics ticks at render rate; smoothing reads stable positions.
Or move camera in _physics_process
Custom camera follow in _physics_process. Same tick as the target; jitter source removed.
Disable smoothing for pixel art
For pixel-perfect games, smoothing is the wrong primitive. Snap to nearest pixel; smoothing introduces sub-pixel positions.
“Render-time interpolation needs render-time samples. Physics-time positions don't qualify.”
If your project mixes 2D camera follow with physics-driven characters, interpolation is non-optional. Enable it on day one.