OK, been lurking in this forum and trying to solve this problem for a while, so I hope this helps anybody facing the same predicament. I registered an account on this forum just to post this.
I use a MacBook Pro 13" mid-2017 with touchbar, and run both operating systems with Bootcamp on Windows 10.
I bought a 'Microsoft Designer Bluetooth mouse' to go with this setup, a product which is advertised as a Bluetooth 4.0 mouse. With this, I could pair to only one operating system - it's either or. It doesn't do both. I tried the linkkey registry trick described in the past pages of this thread, to no avail - I suppose the problem either lie with the fact that this is a Bluetooth 4.0 device which has different requirements for linkkeys, or that Mac OS High Sierra imposed a change in the linkkey procedure as opposed to earlier versions of Mac OS; either way, I couldn't be bother to solve it from a code perspective as I'm not very technically minded.
What followed was that I bought another mouse, which looks similar to the Microsoft Designer Bluetooth mouse I have, but is supposedly an unbranded OEM mouse which claims multi-device support. I first paired it in Windows 10, then rebooted in Mac OS to pair, and now it works functionally in both operating systems. (Doing it the other way round, i.e Mac OS first, then Windows 10, renders the mouse unable to pair in Windows 10)
The link to the mouse purchase is here:
https://shopee.sg/product/6078026/100213603/
(This is a Singaporean website, I suppose if you're living elsewhere than Asiam you could find the same model if you google the keyword "VMW-181" on Amazon or such. These OEM products from China seem to be flooding the web and various e-commerce channels under different brand names - but pay attention to the photos and instructions as they are almost always similar.)
The only problem I found with this mouse is the response time - I feel a microlag (about 50-100ms) whenever I activate the mouse after it's been left idle. As it's advertised to be a Bluetooth 3.0 device, I suppose it doesn't have the same Low Energy (LE) wake instant wake capabilities as a Bluetooth 4.0 mouse (my Microsoft Designer Mouse wake-up time was instant without such perceivable latency).
However, between having a Bluetooth 3.0 mouse that can dual-boot, a Bluetooth 4.0 mouse that can only single-boot, and using a Logitech wireless mouse with a universal USB receiver (hence sacrificing one USB-C port on my MacBook pro), I'd go with the first option until a better solution comes out for a Bluetooth 4.0 mouse.
Lastly, since dual-booting has proven to work with this mouse, I suppose it will also work with other Bluetooth 3.0-type mice?
Just a thought
