Is the Magic Keyboard 2024 compatible with a 2012 Mac mini?

Officially? No. Not supported.

The current sold-in-2025 Magic Keyboard (USB-C) model uses a USB-C connector, and the Mac mini 2012 uses USB-A connectors and lacks USB-C connectors.

It’ll probably mostly work, sort of, but it definitely won’t support Touch ID, and you won’t be able to plug it in to pair and to charge it without a USB-C to USB-A dongle, or a USB-A to USB-C cable. Maybe the right dongle or the right cable works, if you can find it. Maybe.

I’d preferably scrounge a gently-used Apple wired keyboard or a newer USB-A Apple keyboard, or new or newer third-party wired keyboard for a Mac mini late 2012. A USB-A PC keyboard will also usually work.

How much do you want to work, and how much do you want to spend on maybe-not-working dongles or cables or USB-C power supplies for charging?

If it's the USB-C one to which Limnos linked, no. It's probably not USB-C, per se. It's the

System Requirements

Mac with macOS 15.1 or later

iPad with iPadOS 14.5 or later

iPhone with iOS 14.5 or later

Apple Vision Pro with the latest version of visionOS

section. Apple has apparently been doing things with their wireless ("Magic") peripherals, whether ones that have the Lightning connector, or ones that have the USB-C connector, that involve more than generic BlueTooth support.

A 2012 Mac mini can't run anything higher than Catalina (10.15.*) and is incapable of running 15.1 (Ventura), so while it is easy enough to get a USB-C (female) to USB-A (male) adapter, you could make the USB connection just to get hung up on the minimum OS requirement.

No for this one, if that's what you mean by a 2024 model --> Magic Keyboard (USB-C) - US English - Apple