Hi. This post is about using an external keyboard with Android. If you use Linux, I'm afraid I can't be of much help.
After pairing or connecting an external keyboard, you may have to set the keyboard layout for it. Android was kind enough to slip me a notification for that purpose, but the setting can be found in Settings > System > Languages & input > Physical keyboard > [keyboard model] > Set up keyboard layouts > [Language of choice] Android keyboard. Please beware that there might be a [Language of choice] Gemini keyboard in the list too, which I suppose is intended for the internal Cosmo keyboard. For me, it gave an incorrect mapping, so stick to the Android variety.
You may stop reading now. The rest of this post is just me rambling about, trying out a few external keyboards I dug out of a storage bin.
I am typing this on an old external Bluetooth keyboard. The sticker on the back says "Linocell art.94059 IK47313". I think that's just something my domestic reseller made up, but it should be enough to find a picture, would anyone be interested. The keyboard is meant for a tablet. As far as I can tell !"#%&/()=+?'*ˆ,.;:-_@£$˜ seems to work for me, but when I press < or > I get an § instead. That kind of makes sense, as the physical layout is a bit odd. The < and > are physically located on a key where I would expect to find § (on a Swedish keyboard). Worse, { [ ] } seems unavailable. Not good for coding then...
Now I'm trying out an old USB keyboard. It's a bit broken, but after setting up the layout, I can now type all the special symbols §½!"#¤%&/()=?+\@£$€{[]}ˆ˜'*-_.,:;<>|
Finally I am trying a "Deltaco TB-109I Bluetooth 3.0 Macro Keyboard", which is a tad silly, as it is smaller than the internal Cosmo keyboard (think media PC remote control). From a typing perspective, it's on par with, say, my old Nokia 5510, which I, back then, thought had a "good" keyboard. This experience is giving me a refreshing reminder of how much better the Cosmo keyboard is than most "smartphone keyboards". Anyway, let's test symbols now: §½!"#¤$%€&/()=-_{[]},;.:'*ˆ˜<>||+?\ well, some keys are in odd places and there's no F12 (not that the Cosmo cares). Oh, look even its square-inch-and-a-half trackpad works, and gives me a cute little mouse cursor on the Cosmo.
In summary, with the correct layout set, I can get external keyboards to work pretty well. Obviously I have only tried Swedish layouts. Perhaps there are bugs in other layouts, in which case some remapping tool would be needed, I suppose.