probably Ethiopia?
Rarest passport stamps

I'd personally say that the Virgin Islands and British Virgin Islands are the two most difficult. I have neither as of now
I have played people (apparently) from both those locations (combined population < 150k), though haven't played anyone from several countries with populations over 20 million, despite having reached 199 passports. Obviously population is one factor, but chess popularity, free time, and internet access are another.
100% yeah. It's strange, cause I do have one for North Korea which my initial thought is that they would be suppressed to not be able to play, which makes sense to me, but I guess not maybe. I've been to the U.S. virgin islands, though, and to be honest, they don't seem to have much internet access

Yeah I don't know how many of the 8317+ people who appear to be form North Korea are really from there as there's a tendency with some to pick random flags for the fun of it. At least 4269+ people have set their locations for the Vatican City, so 5 times the number that currently there. Only 102+ with the Niue flag (https://www.chess.com/leaderboard/live?country=NU&page=3). Just checking the global ranking lists for the lowest number of people probably a good indicator of the hardest passport stamp, assuming each person in each country plays an equal amount of games etc.

It's a shame people choose random flags. I'd really rather play someone from Vatican city for real. Getting your bishop captured by a bishop is funny to me.
It's a shame people choose random flags. I'd really rather play someone from Vatican city for real. Getting your bishop captured by a bishop is funny to me.
Backstabbing!
I never could think that'd happen
I agree with you. Getting a stamp from real Vatican is better than a fake.
I know someone from Vatican. Cool guy.

Kathmandu
thats not a country, thats the capital of Nepal
Has a flag though! https://en.wikipedia.org/wiki/Kathmandu#/media/File:Flag_of_Kathmandu,_Nepal.svg

How would someone get to play from North Korea?
One does not need to play from North Korea to have that flag. It’s a choice to select that flag. You just need to play with someone willing to put North Korean flag…
Vatican City