When creating a new item in SP Simple Portfolio, if you use a webp image it throws an error on save:
0 imagecopyresampled(): Argument #2 ($src_image) must be of type GdImage, null given

It does seem to save changes though.
It also seems to cause a problem (potentially) if you try to edit an item using PageBuilder from the list view. It just opens a blank page. But I haven't worked out if it's due to having any webp images set in the main and/or thumbnail image blocks or if it's another issue altogether.
I'm starting to suspect that there's an underlying issue where after you edit using PB the first time and save everything, if you go back to re-open it to make changes (using the Edit with SP PageBuilder button in the list view), it white pages. Error reporting and debug aren't logging anything for me when it fails.