Yeah, I found that out. WebP is great and gives good compression, but the resolution limit makes it difficult for larger maps. I've had some luck with splitting the larger maps into quarters. I've then uploaded them to my VTT of choice (Foundry) and then put them together once uploaded. You might also check to see if you can use zero loss JPG format. You still get decent compression, but you don't get the little pixel artifacts that show up when you zoom in. Anyways, just suggestions. Keep up the great art regardless!
Morgan