Drop AVIF images above, download PNGs with transparency kept. Conversion runs in your browser and the file stays on your machine.
When PNG is the right call: the image has transparency to preserve, it is heading into further editing, or an uploader accepts PNG and not AVIF. PNG is lossless, and repeated saves cost nothing.
When it is not: photographs heading to email or chat. PNG stores photos expensively, and a photographic AVIF can grow 10x or more on the way through. For photos, AVIF to JPG gives a far smaller file for a loss you will not see.
Why AVIF exists: it is the format modern sites serve to load faster, holding an image in roughly half the bytes of JPG and a quarter of PNG. That makes it excellent to send across a network and awkward the moment it reaches older software. Converting a copy is the fix, and the original AVIF stays your compact master.
Sharp edges survive. Logos, screenshots and diagrams come through crisp, because PNG never smudges a hard boundary the way lossy formats can. Fine text stays readable at any zoom.
Batches are fine and every file shows its own before and after, worth watching here because a photographic AVIF can come back several times larger than it went in.