Biden could approach and pay respects, but WAS NOT allowed to 'lay' the wreathe
For comparison, here are past presidents, actually elected and recognized by the US military as their commander in chief. Wreathe is presented for the POTUS to lay, rather than already there to begin with.
Here's Trump
And Obama
And Bush
And Clinton
And Reagan
Only Biden was denied the laying. Could approach and pay respects, but not lay it. Aligns with being a foreign dignitary rather than the POTUS.
I made a similar assumption.
While it seems any citizen can apply to lay a wreath, I found no video in searches for foreign dignitaries, ambassadors, or heads of state doing so. But admittedly, those may not have been video recorded or uploaded. Even finding presidential video was not easy. YT only wants to show you Biden and Trump.