The keyboard will connect to the computer, so can’t the mouse piggy back on that wire by plugging in through the keyboard?
Edit: Turns out I just never knew they exist all over the place. Thanks! Learning a lot of cool new keyboard features out there.
Interference is a legit issue, especially if there is an active USB3 port near the mouse dongle. This is because USB3 specifically does create some mild interference near the 2.4GHz range used by the wireless mouse. The back ports of the motherboard also sit with the metal box between the dongle and the mouse, blocking some of the signal. Using a box-front port, or a keyboard port as you did, helps separate the dongle from potential interference sources. Even just a few inches helps a lot.