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.
One thing I've gained from reading through all of these things the past few days is a whole new respect for the Military and how they all adhere so strictly to codes and traditions. It's comforting to know that there are so many people in this world who still hold something sacred. There was a video yesterday of an older gentlemen delivering packages, saw someone's flag fall on the ground and, despite the fact that it obviously caused him physical pain, he picked it up off the ground, folded it perfectly and saluted it. Literally made me cry, thinking about what people have given up for that flag and how we are so close to losing it all.