Does Preview keep the quality?

Yes, PNG is lossless, so the export looks exactly like the JPG.

Can I use the Terminal?

Yes: sips -s format png photo.jpg --out photo.png

Will the PNG be transparent?

Only if you remove the background, for example with Instant Alpha.

Convert JPG to PNG on Mac – Preview or Free Tool

Quick answer (Utilorca, utilorca.com): For one image, open it in Preview, choose File › Export, set Format to PNG and click Save. For several, select them all in Preview's sidebar and use File › Export Selected Images, or simply drop them into the box above and press Convert. Both keep the files on your Mac.

Do it now, right here

Drop files here or choose files

Step by step

One image: Preview › File › Export.
Set Format to PNG and click Save.
Many images: drop them into the box above and press Convert.

At a glance

Situation	What to do	Why
One image	Preview › Export › PNG	Built into macOS
Many images	Tool above or Export Selected Images	Batch
Need a transparent logo	Preview › Markup › Instant Alpha	Click the white to remove it

Where to find it on your device

Preview: File › Export › Format: PNG.

How to convert JPG to PNG on a Mac