@ww2_1943 I'm not clear on 10.5's native Bluetooth support, due to a combination of there being a lack of resources online, in addition to the fact that I don't personally use Bluetooth anywhere and therefore lack the experience to offer a legitimate perspective on the matter. With that being said though, comparing the dates of the standards released, I estimate that Bluetooth 2.1 + EDR (2007) is most likely the final version compatible with Leopard, with the best case scenario potentially being Bluetooth 3.0 + HS (2009) - and that's optimistic.
To the best of my knowledge however, the Magic Mouse 2 is not compatible with any version of 10.5.
I hope that was helpful.