Unifying definitely lets you pair multiple devices (keyboard, mice) to the same dongle, but I'm less sure about whether it lets you pair multiple dongles to the same device(s) and then hot switch between them.

I have been all-in on Logitech keyboards and mice for years now. In the beginning it was just the unifying receiver but they've recently switched over to the Bolt receiver. Unfortunately the Bolt receiver is not backwards compatible with devices made for the unifying receiver.

You can pair a single device to multiple receivers and the "switch" button on each device will let you cycle between each receiver. I use the same keyboard and mouse with both my personal computer and my work computer. Every time I need to switch, I just need to use the device switch button on the keyboard and the mouse.

Any Logitech device that supported both Bluetooth and Unifying, such as the MX Master, allowed you to cycle through up to stored 3 connections of either type. The older, cheap devices generally only had a single connection.

Logitech also makes or made keyboards with 1-2-3 hot swap keys that allowed quick switching with a single press.