Tried pairing a MX ERGO and MX Master 3 on Ubuntu 20.04 and neither was recognized.

The Unifying Receiver is a work-around, but it's surprising and somewhat inconvenient that these two premium mice don't do something as simple as support Bluetooth pairing on Ubuntu.

Competing products like Kensington Expert Mouse Wireless Trackball do.

And don't get me wrong, I understand that the Logi Options software doesn't work on Ubuntu. However, I'd expect either MX mouse to be pairable as a simple Bluetooth mouse without the full feature-set, just like it works on Windows.