PNGs will persist because I know that they're lossless by looking at the filename. When I hit File > Save as .png, I don't have to inspect output metadata (that image viewers don't expose) or play around with exporter settings.

It's unfortunate that we didn't give lossless webps a separate extension. Frankly I think even saving them as .png would've better than what we have now - people roughly understand that a .png is an image without artifacts, and any self-respecting image viewer will inspect magic bytes before opening a file anyways.

Well, you should enable Adam7 interlacing for nicer progressive decoding!

I suppose it's not very useful nowadays as most any image will load fast, though.

Being lossless is a function of the whole pipeline from an input image to an output image. The last step being encode to PNG doesn't guarantee anything about losslessness.