Rarely these days do you find a real Bluetooth only mouse. Many are multi mode. Frequently you will see tri-mode rechargeable mice, wired direct use plus recharge, fast refresh 2.4ghz gaming dongle, and bluetooth for travel with a laptop.

I’ve always assumed the expect the dongle on a gaming desktop and Bluetooth with a laptop as laptops usually have dual mode WiFi cards, but many desktops come with WiFi now also.