I'm A Banana
Potassium-Rich
Implying that spell scrolls are magic items
I understand that there is no "Magic" action listed under Spell Scrolls in the PHB but they are magic items that cast a spell, casting a spell is considered to be the Magic action
Yeah, spell scrolls I'd think are magic items.
But the Magic action is used for two distinct purposes. One is to cast a spell. One is to activate a magic item. Fast Hands lets you do the latter as a bonus action. Using a scroll is the former, which Fast Hands doesn't let you do as a bonus action (though Quicken Spell does, in certain circumstances, for a cost).
Pretty clear RAI there, given "free Bonus Action casting of every spell in the game" almost certainly wasn't the intent behind a level 3 rogue ability. I can see some tables ruling differently based on the fact that casting a spell is ALSO a Magic action, but that's not clear RAW, and I wouldn't allow that at my tables, because not every magic item is used with the Magic action.
Like, I also wouldn't let this mean that rogues could attack with a magic greatsword as a bonus action, even though you definitely activate a magic greatsword by trying to hit someone with it!