migrating an Aperture library to the Photos app

It should work on Big Sur as well.

Basically, launch the Photos.app while holding down the options key ⌥, until you are seethe Library chooser dialog, the release Options and select the Aperture Library from the dialog.

Then wait, it may take a long time, if your aperture Library is large.

But, if you are already running Big Sur, you have missed the chance to run Aperture before the migration to get your Aperture Library ship-shape. if you did not yet tell Aperture to create high resolution previews for all edited versions, you will not be able to save your Aperture edits in a high quality. You will only migrate the original image files and albums to Photos for Mac.

Can I suggest first making sure you have a backup of the aperture library before converting it, in case the conversion goes wrong.