Grammarly website: "You can upload a document which size is under 4 MB." Is this grammatically correct?

On the Grammarly website, they have the following sentence:

You can upload a document which size is under 4 MB

As a fan of irony and grammar, I'm curious as to whether the bolded portion is grammatically correct. It sounds really awkward, and I've honestly never seen anyone use that phrasing. I would've opted for one of the following:

You can upload a document whose size is under 4 MB

You can upload a document which has a size of less than 4 MB

You can upload a document with a size under 4 MB

You can upload a document smaller than 4 MB

Is their version acceptable?

As Janus Bahs Jacquet observes in a comment beneath the poster's question,

Your instinct is correct. Their version is not.

Tacitly (and belatedly), Grammarly seems to have recognized the ungrammarliness of its originally posted wording. The wording that now appears on the cited support page is

You can upload a document of 4 MB or less.