Thank you.
The Seal of the President of the United States is fully defined in the CFR.
It must be used in that fashion [only] when on US soil.
Changes indicate it is not on US soil and that there is reason to obfuscate the person, place or speech of the POTUS.
There can be explained by NatSec concerns.
My initial guess is that Biden wanted the optics of himself behind the seal but being on foreign soil, the conference frowned on the official seal. So they made up a non-descript plaque.
Maybe the muzzards, knowing full well he's a fake, outright refused to participate in the charade.