Not only hieroglyphs can be used for the meaning and the sounds of a word, they often use both at the same time: the rebus principle, or "represent something by what it sounds like". That's a lot like writing English "I see you" as "๐๏ธ C U".
Coptic, mentioned in the video, is a descendant of Egyptian. That's why Champollion's strategy worked: even if the Coptic translations of the Greek words won't give you the exact sounds Egyptian used, at least it allows you to see consistent patterns, that you can contrast with Egyptian loanwords in other languages.
For reference on dates, Ptolemy V reigned from 204 to 180 BCE. He's the grand-grand-grandfather of "that" famous Cleopatra (Cleopatra VII Thea Philopator).
I'd argue Demotic isn't quite a different language from the Egyptian written in hieroglyphs; both are more like different registers of the same language, written with different writing systems. So it's less like 2025 English vs. Old English and more like "colloquial 2025 English" vs. "a really posh 2025 English", with one being written with Latin letters and another in Saxon runes.