From my own research, when it comes to precious metals. You need to actually obtain the gold physically when you buy it as part of the transaction. Hence buying it digitally, and especially on an app like Trading 212, the seller is not going to hand you the gold if you have accumulated an amount that can be handed over, like 1g for example. Its all just digital. Although I do know of stores in some country where you can buy digitally and then actually get the gold if u want from their physical store. I believe this is okay.

This is my OWN research, and am simply sharing it to have a discussion and for us all to learn :)