I have one online friend that moved to Monaco.

I've met people claiming to be from Estonia, which I'm not even sure what continent that's on.

For me, it's gotta be Namibia. It's a country in Southern Africa, and the only reason I've come to be aware of it was because I've made a very fortunate contact whilst talking on amateur radio. Two consecutive Decembers I happened upon the same gentleman on the 10 meter band, and he confirmed my QSOs (contacts) on the logbook!

Probably contested region of Kashmir with someone in a mobile game, and a guy from Ukraine I knew before the war because we both made some similar uploads on YT. I got a book from a guy that I met on reddit that turned out to be the author and was from somewhere in central Africa, but I forget where exactly. As far as on Lemmy, this one girl from Turkey was fun to talk to. Most people here do not share that much personal information.

Lesotho

I was in a hobby secret santa organized online - I got two presents that year, some very generous hobby additions and the discovery that San Marino isn't just a region in Italy...

Met two people from Transnistria, one from the Isle of Man and one from Micronesia. I wouldn't say they are super rare but I'm quite sure most American would consider these fictional countries.

My neighbors are from Chuuk Lagoon

I wanna mention any of the 81 micronations... (like Christiania, Liberland or Asgardia) but since they're so novel, they're probably not the most unheard of.

How about some potential future countries... [Heh. They'll be lesser heard of, surely. Is this cheating?]

Like any of Orkney or Shetland, (when they each take a leaf out of the Faroe Islands' book, and declare themselves independent (~ or at least autonomous), fed up with both the UK and Scotland) (or Cornwall (similarly)), Catalonia (will they go for independence already?), Western Sahara (will they ever get past the geopolitical difficulties of the area?), Bougaineville (since they already did the independence vote, will they get things sorted already?), New Caledonia (they keep tryin), Chuuk (will they solve their challanges to?), Rif Republic (oh yes please... tell me they'll start making and exporting hash big-time again), or maybe even Jan Mayen (I've not heard any talk of it going independent, I just think that'd be cool, and people do "live there", for some of the time)...

Or whatever countries exist (secretly) or will exist, on Luna (or... on Calisto? Or Enceladus?)

Have heard of people being from these places. Cannot corroborate for the moons. But there are rumours.

Does anyone live on the Dominion of Melchizedek, Talossa or Westarctica?

Total number of recognised countries in the world's oft said to be something like 195 to 200. If we included all the micronations and places verging to independence (or at least autonomy), it's nearer 300. Without looking up any (last time I tried), I struggled to get to 150. Could be an interesting video documentary series (well edited), to see how many "the man on the street" can get to, in various places. Would anywhere do worse than USA?

I coulda answered simpler, just picking some tiny pacific island nation, or one of the tiny nations embedded in South Africa. Though small size is likely a weak correlate to "most unheard of". Malta? Lichenstein? The Vatican? Ooh, or how about any of those Central Banker areas carved out of countries to make their own country with their own rules and police etc, siphoning off the wealth of the nation they're carved out of? Like "The City Of London".

I've met a person from Kiribati. It's looking bad for them there, we're making entire countries disappear due to climate change.

I've met people from those really small Oceanian countries like Fiji and Tonga.

My former boss is from Suriname. Had never heard of it before working for him, or since then.