Hey, long time lurker here
I've seen a lot of similar conversation around this with other influencers (mainly in the beauty community) so have done some research on the FTC rules myself, and in my opinion the legality here is incredibly sketchy at best. #ad is covered by the endorsement guides section of the FTC guidelines and any disclosure of endorsement must be "clear and conspicuous" for it to satisfy the law. The idea is that if someone is looking at the endorsement, the #ad can't be easy to miss.
White on white, tiny, in a hard to read font, in a corner, behind a white icon is neither clear nor conspicuous (in fact the guidelines specifically state the importance of using clear fonts, clear positioning, and contrasting colours to backgrounds as these are the oldest tricks in the book
Also this disclosure is doubly relevant as grace has previously been known to provide opinions on goods/services without endorsement, and could be classed as a product reviewer. An example of this kind of relationship between influencer and consumer is specifically highlighted in the FTC guidelines and even includes the example of use of a gifted product.
So yeah, sketchy as hell, and generally not a good look...