Welcome to the forum.
In answer to your question, for larger radii on large and unwieldy workpieces I use Woodhaven templates with a hand held router and the large pattern bit pictured.
These clamp to your workpiece using the white index pins on the template to index the template to to to 90° corner of your workpiece and guide your router for a precise radius.
For smaller radii on smaller workpieces I use washers to mark the desired radius, trim off the majority of the waste using a jig,miter or small cordless circular saw staying an eighth inch from the line on the waste side and the bring the cut to the line using a bench top belt sander.
A stationary or bench top disc sander works for this purpose as well.
After you have a finished the radius you may want to soften the top and bottom of the edges of the workpiece using a roundover router bit.
This is a bit tricky using a hand held router on smaller workpieces so for these I suggest using a router table.
Larger workpieces can be clamped securely to your bench when using a hand held router.
You can also soften the edges of your workpiece with a bench plane and sandpaper or just sandpaper on a sanding block made from any scrap of wood.
Hope this helps.
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