JPG to PNG files are extreme large after exporting

Another possibility is that is is caused by the way jpg and PNG compression works.

Jpg compression works best with continuous tone photographs, whereas PNG works best with flat like colors, like in graphics.

I exported the image below at full resolution (8256 x 6192) at 60 quality as jpg, and the file size was 8 MB.

Then I exported a full resolution PNG from the jpg,  and the file size was 74 MB as 8-bit and 157 MB as 16-bit.

This image has lots of sharp, busy detail, which doesn't compress well with the PNG format, which explains the large file size.

Generally speaking, the jpg format has very efficient compression, with some quality loss. (lossy compression).

The PNG format uses lossless compression (no quality loss), which doesn't work well at all with sharp, detailed photographic images, resulting in large files.

A likely reason is that you have either Content-aware Heal spots and/or are using AI masking on the image, AND you are exporting with full metadata. When you choose to export all of the metadata, the binary masks are included in the file and can greatly increase its footprint on disk.  Try dialing back the metadata you are including with the file. 

What are the pixel dimensions of the original jpg?

Please post a screenshot of your export settings, with the same sections visible as in my screenshot below.

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