It’s really hard to say without knowing what threats you’re concerned about, but I’ll share some information about the security of the wireless connection itself at least.
While Bluetooth isn’t great, I would never choose some random home-brewed protocol over a 2.4 GHz dongle before modern Bluetooth. With those USB dongles you don’t even know if the connection is encrypted, which is going to be the most important thing here.
Bluetooth has had mandatory encryption for basically forever, so unless you find a Bluetooth device that’s like 20 years old they’ll always be better than some unencrypted USB dongle. The main security issues with Bluetooth typically surround the pairing process, so probably don’t do that in public.
There haven’t been any significant security improvements to Bluetooth since 4.2 as far as I’m aware, so aiming for a Bluetooth Low Energy 4.2+ device at a minimum is what you’d want, but there’s no reason to not buy BLE 5 devices in 2023.
Apple’s Magic Keyboards and Mice operate securely, as do Logitech’s Logi Bolt devices. I’m sure there’s plenty of other options too.
Privacy Guides will not be supporting companies (Reddit) who actively harm the privacy of their users, but r/Privacy should still be open as far as I know? We have nothing to do with r/Privacy though, so if you’re having trouble posting there you should contact their mods.