How does that work exactly? AFAIK, imbue is not a "term of art" in 5e. Does it consume a spell slot? If so, is the slot expended when you imbue the spell or when you cast it? It seems to me that the implication is that you use up a slot when you actually cast the spell, but I'm not 100% sure.
My read is that "imbuing" is defined by the feat, and so that doesn't take a spell slot.
"Cast" is where I'd rule the spell slot is spent.
It's also a little wild that this lets you access any spell on your spell list. Not powerful, exactly, just...weird.
"I'm Jeormy the Wizard, and I have heard of this 'fireball' spell, but I haven't studied it. But here, I drew a picture of a fireball, and now I can cast it!"
"I'm Sneaky Doug the Cleric, and while I didn't pray today for a cure wounds spell, I did draw this cool S, and that can heal some wounds real fast!"
"I'm Velma the Sorcerer and here's a drawing of a spell I don't know how to cast and will now cast fast."
IDK, a lot of this book seems a bit half-baked to me, so not SUPER surprising there's a half-baked feat in there, too. Being able to cast any spell on your spell list isn't broken (the game-design-y assumption is that a player does have access to whatever the most powerful spell of any given level is, and this doesn't break that assumption, it just makes it more likely), but spell lists are pretty grounded in the diegetics of your character, so this raises the in-world question of
how you're imbuing the card with magic you don't know. Bleh.