Rollpie Favicon is a free favicon generator that runs in your browser with no install. Upload a single image and it creates the whole set of favicons your website needs, ready to download as a ZIP.
In the design panel, choose Placement or Background and the values appear in the child panel beside it. The mode is crop, fit, or drag, and with drag you can fine-tune it using the zoom and the X and Y values. The background can be transparent, white, or a custom color.
Use the wheel to zoom the board and drag to move it; the zoom level sits at the bottom right. Check how the icon reads in a light and a dark tab in the preview panel, then save it with Save ZIP in the file panel. It contains the PNGs for every size, favicon.ico, site.webmanifest, and a snippet with the link tags.