New iMac. Mouse frozen in left corner

Plugging the mouse to your iMac with the supplied Lightning cable is not just for charging, but to also perform a hardline pairing to your iMac. It's possible that the mouse lost its connection to your Mac for some strange reason (it happens) and plugging it in for a moment re-establishes the connection. It's only for a couple seconds.

Johnb-one,

This is how the Magic Mouse 2 charges:

jkurly,

I assume you saw the power switch. If you have an old USB wired mouse lying about, it should work on a basic enough level to finish setup and see if the Magic Mouse 2 waked up.

Hi, jkurly… try turning off the mouse( power switch on bottom of mouse) waiting about 10 mins; then turn it on again… you could use it with the supplied cable as a wired mouse…

jb