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.
The military branches also did NOT lower their flag colors when Biden approached the Wreath which is a mandatory part of the ceremony. Biden is not POTUS.
I think that's only for when the wreath is layed, and not necessarily when someone approaches to pay respect. At least, that's what I gather from videos. Trump when 30 minutes late to a wreath laying that had already been performed (memorial day, was happening whether he was there or not) approached post-laying without colors being lowered.
But damn good eye.