WebP also has a near-lossless encoding mode based on lossless WebP specification that is mostly unadvertised, but should be preferred over real lossless in almost every use case. Often you can half the size without additional visible loss.
Is this mode picked automatically in "mixed" mode?
Unfortunately, that option doesn't seem to be available in gif2webp (I mostly use WebP for GIF images - as animated AVIF support is poor on browsers and that has an impact in interoperability)
Not in gif2webp, no. It is available in img2webp as a global (not per-frame) option. It looks like when you pass it, it will be used for all lossless encoding, including when "-mixed" tries the lossless mode.
WebP near-lossless is very far in compression density against that kind of visually lossless. Still 2-3x more bits I think. No reason to compare. The near-lossless (at settings 60 and 80) is closer to pixel perfect no matter how much you zoom, whereas Jon's "visually lossless" is what I'd rather call usual very high quality lossy without pixel precision guarantees.
WebP also has a near-lossless encoding mode based on lossless WebP specification that is mostly unadvertised, but should be preferred over real lossless in almost every use case. Often you can half the size without additional visible loss.