Certainly, you can use an Apple Mac Mini with a monitor from another brand, such as LG. The Mac Mini features various ports, including HDMI and USB-C/Thunderbolt, that allow for easy connection to most modern displays. The main considerations are to make sure that:
1. The monitor has compatible ports or that you have the necessary adaptors or cables.
2. The monitor supports the resolution and other features you may need for your workflow.
Switching to a Mac Mini with an external monitor can provide you with more flexibility in your setup and could be more cost-effective than purchasing a new iMac, especially if you already have a monitor, keyboard, and mouse.
Alternatively, if you're considering a laptop, a MacBook Pro with a 15 or 16-inch display can be a good choice. They are powerful machines and offer the added benefit of portability. You can also hook up an external monitor to a MacBook Pro when you're at your desk, giving you the best of both worlds.
So both options are viable; it mainly depends on whether you require portability or not.