My wife's last name is only 2 letters long. Some websites don't accept that as it's too short (take that, Xi Jinping!)
Conversely, I've had to fill forms in Korea that included space for only 4 letters, including both first and last name. Needless to say, my 3 first names plus last name didn't fit.
When my father was born, his parents gave him a normal given name, but endowed his middle initial as only a single letter. They said, when he grew up he could choose whatever name fit that initial.
The initial happened to match his father's given name, and when he was old enough, he reliably chose to take that name as his middle name. It is certainly an endearing story of filial devotion, and a distinct lack of finicky SQL databases or web input validation in the 1950s.
My first and middle names are both relatively long - this caused me issues when getting a US SSN. On a UK passport they are both in the “Given Names” field - and both ended up on my I-94. This was too long when the person at the social security office tried to enter my details. They had to send it by mail to be processed which took something like 6 weeks…
I have a legal name in Chinese. It is very weird to call people by full name so everyone picks their own English name. Nobody calls me anything other than the English name since I’m 10 year old or so except maybe from parents.
Moved to UK last year. Couldn’t put my English name in anywhere and had to use my full name. Feels super weird getting called so.
Same in Japan. My name is truncated on nearly every single form I receive from utilities companies. online forms will regularly limit your full name to 9 kana in total.
The good news is that for most of those Korean forms the limitation/validation is only on the frontend, so a quick "inspect element" and some HTML editing solves it.
Conversely, I've had to fill forms in Korea that included space for only 4 letters, including both first and last name. Needless to say, my 3 first names plus last name didn't fit.