Hieroglyphs and kanjis are still linguistic in nature. So no matter how you write a specific unit it’ll be interpreted the same, as long as recognisable as that unit. Here’s a Japanese example:

sure, they’re written in slightly different ways, but they’re still the same ⟨愛⟩ /ai/ kanji, so it’s still conveying the same meaning (love, affection).

Emojis on the other hand aren’t typically used to convey a language, even if conveying meaning and found alongside language. That’s what makes them paralinguistic (beyond language), they’re a lot more like “mmhmm, ah!, ahn?” grunts or Italian hand gestures than like kanji or hieroglyphs. And in this sort of paralinguistic system, even little changes on the symbol change its meaning.

And… well, that’s what we’re seeing here, and the likely reason YT replaced unicode emojis with images. For me at least it’s convenient, might as well uBlock them.