I'd like to use the "find my PC" feature on all my systems, but does that feature have a hard requirement of needing an MS login?
The Microsoft 'Find and lock a lost Windows device' article says
Getting started with Find my device
You can only use the Find my device feature for Windows devices. You can't use this feature for iOS devices, Android devices, or Xbox One consoles.
You must be signed into your Windows 10 device in order to lock and locate it with Find my device.
You can't use Find my device with a work or school account. Your Windows device must be connected to the Internet and have enough battery power so it can send its location.
So the answer is yes, you'll need to sign-in.
You will need to login into any service that tracks your computer. This may be Windows itself or any other service.
If you don't like Microsoft's login, here are some alternatives: