I like webp for space and bandwidth reasons (300 KB PNG -> 35 KB webp) but support among applications/services seems spotty.
Like, my phone's gallery supports webp no problem. But Google Voice or my phone's SMS app will not handle them at all. I don't have a converter app, so I open it in gallery, take and then crop a screen shot if I need to send it to someone (crude but effective).
With Lemmy, a lot of admins force conversion of uploads to webp on the backend to save storage costs and reduce bandwidth. If you want to get a different format, such as png, you can add ?format=png to the end of the image URL. That's one of the options I'm working to add to my custom UI (download image as [webp, png, jpg] ) because I've run into the same problems as you when trying to share things from here.