Quick answer: Construct 3 custom shader output appearing pixelated at zoom? Effect renders at base resolution; upscaled - render the effect at output resolution.
Glow effect on a 100px sprite; zoom to 4x; glow stays 100px-wide and visibly upscaled.
Render at target resolution
Custom render-to-texture at full screen size; sample at target.
Or use post-process
Whole-screen post-effect at screen resolution; not per-object.
Author at higher base
If glow is for a sprite, author the sprite larger; downscale.
“Effect resolution and zoom interact. Plan deliberately.”
For pixel-art games with effects, the resolution decisions are upfront.