It’s a better format than JPEG, GIF, or PNG, while doing the jobs of all of those, but better (in most cases), and is an open format. It also has wide compatibility nowadays. The only major downside is a lot of social media services don’t even think about it being a potential format due to a lack of awareness/wide usage, leading to a degraded experience when someone shares a WebP somewhere (lack of auto-embedding as an example). I suspect this is why it gets a lot of hate here, which is unfortunate because it’s not at all the fault of the format.
AVIF (based on AV1) is the up-and-coming format that beats WebP in most cases now, but support isn’t quite there yet (mostly due to Apple), and it has the same problems for social media as WebP. However, it doesn’t have any true lossless mode AFAIK. HEIF (based on HEVC) is also good, but is heavily patent-encumbered and not as open. JPEG-XL is dope and potentially even better in some aspects, but has very poor support across the board.
WebP is not proprietary. It’s an open format, is not patent-encumbered, and its reference implementation/libraries are open-source. It is driven mostly by Google, similar to Chromium.