PNG, WebP or AVIF: which to export
All three formats keep transparency, and all three open in current browsers. They differ in how small the file gets, how long it takes to make, and which other apps can open it.
Three formats, three jobs
PNG is lossless: every pixel comes back exactly, which suits screenshots, logos and anything with sharp text, but photos saved as PNG are large. WebP is the everyday choice for the web: a photo is usually about a quarter smaller than a JPG that looks the same. AVIF is smaller again at the same quality, but it takes longer to make, and some older apps and email clients cannot open it.
The one that breaks transparency
JPG has no transparency at all. Export a cut-out or a logo as JPG, and every clear pixel is filled with a solid colour, usually white. Keep JPG for photos that fill the whole frame and must open everywhere.
The three steps
Converting a JPG to PNG does not bring back lost detail or transparency. The new file is larger and looks exactly the same.
Then what
When the file also has to be smaller, Optimize image resizes it to the edge length a page needs as it converts. For a product photo that needs a clear background first, Remove background cuts it out, and PNG, WebP and AVIF all keep the result.