VP8 is in all major browsers due to WebRTC, and webp uses little more code than the VP8 keyframe decoder, so it also has baseline support and is unlikely to be deprecated any time soon. https://caniuse.com/?search=vp8
Similarly, AVIF uses little more code than the AV1 keyframe decoder, so since every browser supports AV1, every browser also supports AVIF.
I don't know much about webp other than you get about 50% savings in compression vs png/jpeg, but it does have some hard limits on sizes of images. It doesn't do well with webtoon reading formats (long strip format).
Otherwise, I love webp and use it for all my comics/manga.
Even nowadays, webp seems to be good specifically for its lossless mode. It seems to create files that are substantially more efficient even when compared with advanced png encoders. For comics, png should probably be used over jpeg, so webp is likely indeed an upgrade, aside from compatibility.
For photographs, jpeg has really been optimized without reducing compatibility, and also in another less compatible way (incompatible viewers can display it without erroring out, but the colors are wrong) and there's such an encoder in the JPEG XL repo.
It was mostly about compatibility but looks like photoshop supports it now so I guess I can now officially say I don't really care one way or the other.
As for JPEG XL, of course they unkilled it. WEBP has been deprecated in favor of JPEG XL.