I don’t know what a .webp file is but I don’t like it. They’re like a filthy prank version of the image/gif you’re looking for. They make you jump through all these hoops to find the original versions of the files that you can actually do anything with.
If I remember it correctly you can’t rally beat a good dictionary encoding with wavelet compression for certain kinds of image such as drawings, cartoons and in general images with no or flat shading.
(Might be a bit outdated on that believe as I don’t really know what compression algorithms are used in JPEG-XL or WebP)
Further, GIF is lossless compression, so that means your drawing compressed with it will be much smaller and after decompression you still have the same image exactly, pixel by pixel.
That said, most drawings nowadays being digitally created with vector drawing apps means that an even better format is whatever native vector graphics format used by the app as that can scale to whatever size you want.