I found some notes on the problem that I had written some years ago when it happened in another release of Mint.
In My case it was that on 'some computers' it actually matters which USB port the USB wireless thingy is plugged into. At the time it was a known Logitech thing.
It might be worth exploring, by trying each USB port in turn for a day. In my case it was one of the rear ones that was the recommended port to use. I had assumed using a front one closer to the keyboard and mouse would be better.
On my secondary computer, the rear ones cause glitches - but the front one works with a different Logitech keyboard - although because I now run all my computers through VNC, I had to actually set that machine up with a monitor, mouse and keyboard to find out.
At any rate, as fast as I can type now, the keyboard seems to be keeping up.
BTW, I checked and saw that Logitech (at the time) suggested this:
If you're experiencing connection issues with your keyboard, please try the following troubleshooting steps that may help you find a resolution:
Wireless connection
Make sure the device is fully charged (replace with new batteries if it's not a rechargeable device).
Plug the receiver into a different USB port on your computer. If possible, don't use a USB hub or other similar device.
If you are using a USB 3.0 port try plugging the device into a USB 2.0 port.
Try reinstalling the Logitech Connection Utility software and re-pair your device.
Try testing the device on a different computer.
Disable USB Selective Suspend:
Click Start > Control Panel > Hardware and Sound > Power Options > Change Plan Settings > Change Advanced Power Settings > USB Settings > USB Selective Suspend Setting
Change both settings to Disabled.
While at the time this was not actually answering a keyboard lag question, it and another more specific reply prompted me to explore USB ports with the WiFi dongle.
