What is AVIF?
AVIF is a still image squeezed with the AV1 video codec, and it compresses harder than anything else in wide use - frequently half the size of a JPEG that looks the same. It handles transparency and high dynamic range. Support is good in browsers and patchy everywhere else, which is usually why people convert out of it.
What is TGA?
Truevision TGA is a fixture of game development and 3D texturing, where its straightforward layout and real alpha channel have kept it in use long after browsers stopped caring about it. Files may be raw or run-length encoded.