Smart filter
A smart filter is a filter you apply to a smart object that stays editable afterward. You can change its settings, toggle it off temporarily or remove it entirely. That keeps a blur or sharpening fully non-destructive.
First convert your layer into a smart object, then every filter you apply becomes a smart filter automatically. A list of filters appears under the layer, with its own mask strip to limit the effect locally. Double-click a smart filter to re-enter its values, like the radius of a Gaussian blur. Tip: use this for sharpening as a last step, so you can fine-tune the amount later.
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.