Yooo, I've been so frustrated with Logitech! I have an MX Mechanical Mini keyboard and MX Ergo mouse. For some reason they don't pair to the same dongle because the dongles are different and not interchangeable. In addition, whatever dongle is plugged into the right USB-A port of my laptop always lags for some reason. Does Solaar solve those issues?

Solaar mostly changes configuration and helps pairing devices, but it's not part of the drovers, so it might not help you. Anyway I dump some info about dongles here just in case, if you find your devices are compatible you might use Solaar to reset the pairings.

IIRC, there are three types of dongles: the old basic ones, that only work with one particular device, the not-that-old "unifying" dongles (they have a red logo with a star or ray of light), and the new ones that are called "bolt" (green logo with a bolt in it).

I have mostly experience with the "unifying" receivers. Those can pair to any "unifying" compatible device, and keep connections with up to 6 devices. Bolt dongles work similarly but with better encryption.

I've found that using a short usb extension cable with those wireless dongles, rather than plugging them directly into the computer, works loads better and fixed "lag" issues for me. Maybe some kind of EMF interference?

there is an interference from usb to 2.4ghz devices

Also, try using a USB2 port instead of a USB3 one.

USB3's high speed produces EM inference with some receivers.

I can partially confirm: 2.4ghz, or at least the common USB mouse implementation, is very susceptible to interference, it's sent me down a few wild rabbit holes with my Basilisk v3

Same thing helps with USB Zigbee interfaces that use 2.4GHz.

It seems most-useful to make sure it is only a USB 2 cable, without the extra USB 3 data lines.

(USB 3 makes a ton of noise at ~2.4GHz. They could have spread out emissions and dialed them down, but they stuck them in the same trash band that microwave ovens [and mouse dongles] use because... well, it's cheaper and easier that way.]

I had this happen when the dongle is a little loose in the port. Solved lag with a couple of dongles by sliding a tiny bit of paper in alongside it.

The mouse buttons tend to go long before the keyboard, but wireless HID devices tend to be a consumable for most people that use their computer a lot.

We issue the wireless keyboards/mice kit as it is cheaper than swapping a proprietary keyboard in your laptop, and less likely to give users an RSI (really not funny if you are a Jr and have to learn this the painful way.) =3

why not a corded one, if you'll always be using it with a laptop?

In general, for mobile these can get broken up rather quickly, and increase probability of pulling a laptop off a table.

For servers and desktop towers, a cabled solution is more secure... and never runs out of batteries. YMMV =3

If you ever need to do this in future, Logitech have a web only tool that uses web serial to pair the receiver.