Incorrect file and photo dates after iCloud migration to MacBook Air

If you were previously syncing with iCloud, your iCloud sync should indicate the correct date. If you imported the photos instead, the creation date will be the date of import (the original date remains in the metadata).

Which image and movie dates?? Via what workflow?

Are you seeing internal metadata EXIF image dates and related movie metadata dates OR just the fragile file creation & modification dates that are not so important and that can be very fast copied from those more robust metadata dates if the user so wants (with 3rd party tools like GraphicConverter or exiftool).

But sometimes all those dates and GPS are nuked by routing images via social media sites like Facebook, WhatsApp etc so then the user must use a best guess date and GPS instead.

Personally I don't use iCloud Photos but AFAIK it should now better preserve those not so important file dates.

That said, I sometimes also take care that some other documents like plain .txt files preserve their original file creation date so I know when in the 80's or 90's I really created that old file.

See also:

Movie dates and Photos.app - Apple Community

You didn't say how your pictures were "transferred to my new MacBook Air." The best way is to use iCloud Photos. Generally, if you use an Image system like Photos or Preview, you can see when the Image was created. But in a File Management System (like Finder or Windows Explorer,) then you will see when the File was created. That really makes a bit of sense. So, as Matti Haveri said, there are at least two different kinds of creation dates, and you'll see the one that makes sense in the app you use.

With 50000 pictures, it sounds like you need to be using an Image Management System rather than trying to use a File Management System--sort of a square peg in a round hole situation. One of the very best Image Management Systems is included with the Mac-- Photos.

You can import your pictures to Photos, but you may have lost information if you transferred your pictures without staying within the Photos system. Pictures in Photos are not files, so converting them back and forth loses data.