What is AVIF?
Built on the AV1 video codec, and the smallest of the widely-supported image formats by a clear margin - frequently half the size of a JPG that looks the same. It handles transparency and HDR. Being new is its only real drawback: plenty of software still won't open one.
What is PBM?
One bit per pixel - black or white, nothing in between. The most minimal image format in common use, and still the right one for scanned documents, line art and anything headed into OCR or shape analysis. Photographs do not survive it.