As someone who sometimes needs a quick and dirty stock image for my work, webp is the bane of my existence. The work computers won't let me visit sites or install programs/extensions to convert the image, and my document processing programs have no fucking clue what to do with the format. There is an option in Microsoft edge to edit image, and it will dump the result as a .png which is the only workaround I've found.
When I save as an image and it comes up as webp I just change the extension dropdown to all files and change the extension to .png in the filename box, hasn't failed for me yet
Does that actually change the file, or will it still break when your software can't handle webp? Because I did that to a webp, but Firefox still shows it's a webp (in the tab name), probably based on magic byte. I don't have any viewers that can't display webp though, and I think they're all smart enough to go by magic byte.
To be honest I don't know enough about the file types to answer that, but I can confirm at least that a .png I saved from a .webp also says webp image when hovering over the tab if I open it in Firefox.