We investigated this issue and found that this plugin doesn’t replace jpg with webp in AJAX requests at all. We tried to fix this, but we can’t do anything in the theme’s code. We also found similar issues reported to the plugin developers on Github https://github.com/wp-media/imagify-plugin/issues/492
We also checked with the Storefront AJAX shopping cart widget, and the same issue appears there. Here is a screenshot https://monosnap.com/file/RKOmZB2iqAKmcesbkgYpe0ah87WNPP
So we can conclude that it is a bug in the plugin, and it doesn’t support AJAX requests. We don’t have a fix or workaround for this.