There's not much to improve on PNG. It's essentially a zipped up BMP with optional filters to rearrange pixels in a way that will hopefully lead to better compression at the zip stage.
Last time I tested this, if you used xz or zstd to compress a BMP with max settings, it made smaller files than PNG.
WebP solves use cases for both PNG and JPEG as the same format can be lossless or lossy, while getting the benefits of a much more powerful codec.
PNG is good for certain types of graphics. Take a full size 48MP picture and encode it in PNG and it's going to be massive compared to JPEG.
PNG is a pretty simple and effective format but it's not especially good nowadays, there's a reason WebP is popular. Much smaller files for the same quality. Same for JPEG XL.