I just don’t internally see Silvally as a legendary Pokemon. Obviously it officially is.
That's a bit different then simply stating "Silvally isn't a Legendary". One if false according to official sources, the other is an opinion, and an opinion I totally get.
Honestly Kubfu also feels like it's on the same boat. You don't catch it, you're given it. And the lore of Kubfu doesn't make it sound like it's this powerful Pokemon which is rarely seen by humans, but rather is just an aloof Pokemon: while they now live in mountains far from Galar, they used to live there and helped people on their travels.
Silvally and Kubfu feel like "Legendaries" which are specifically made to play around with the idea of what that means. Which is kind of odd, as you could argue it would also be hard to define Mewtwo as a Legendary as its a recent creation. Which is odd, because Mewtwo felt like it too was made to play with the idea of what a Legendary is. In Gen I you have the Legendary Birds which have some loose lore to them, but you got an idea people knew they exist or are said to. But then you encounter Mewtwo, which the only thing known about it are some forgotten science notes and rumors a powerful Pokemon has taken residence in a secluded cave. Yet, without really having a legend, Mewtwo is counted as a Legendary. It's like GF was challenging you to think what is meant by "Legendary"; if it doesn't strictly mean having a legend associated with you, could it be something more perspective like this Pokemon COULD have a legend about it if people knew, a "Modern Legend". But then, Gen 2 until Gen 7, GF seemed to have forgotten that thought and all Legendaries until Silvally were Pokemon which had legends connected to them. Them making Silvally was like them re-discovering the mystery of Mewtwo. And, with that idea re-discovered, and them having also made the Ultra Beasts which a Legendary adjacent but their own group, in Gen 8 made Kubfu, maybe going off the idea of it being some kind of "folk hero", which is a "legend" but not like how its been with other Legendaries before. Hopefully we see this continue in Gen 9, maybe we've already have with the Mascot Legendaries!