Quickly generate asset thumbnails from Viewport Render Image

Add an eye-dropper to the side panel of the Asset Browser.

Click the eyedropper then click a 3d viewport to execute a "Viewport Render Image" and automatically save it as the preview image of the selected asset.

There is an addon that already sort of does this: youtu.be/bewM1-NVac4

Taking inspiration from the outliner's ability to change the tab in the properties editor automatically: maybe if there is a single 3d viewport adjacent to an Asset Library editor, that eyedropper can change to a "refresh" button that automatically uses the adjacent 3d viewport to generate the image.

If an image editor is open, allow drag-drop of the image icon from the top bar of that editor over to the preview image box in the asset library editor.