Yes, and unlike a sign up for a random site, you are actually stating the info and signing the form, it is as "official" a document as a non-notarized/non-certi

Yes, and unlike a sign up for a random site, you are actually stating the info and signing the form, it is as "official" a document as a non-notarized/non-certified one can be, there could be (improbable anyway in practice) legal consequences if you sign something with fake or non-existing data, it is a false declaration. And when you (if asked/needed by the procedure) provide a copy of your ID, you are actually giving them other data points, like your birth date, often nationality, and in some cases even the address of residence.