My legal last name is "Sirén". When I was younger, I almost always used "Siren", because it was easier to type. Then, ~15 years ago, I started noticing that American websites sometimes rejected it, because they considered it inappropriate. Sometimes "Sirén" would work, sometimes it worked but caused minor annoyances, and sometimes it would not work for technical reasons.
Both versions work most of the time these days, but I still run into trouble once in a while no matter which name I use.
Totally agree with the sentiment. It has gotten a lot better in the last 10 years. Very frustrating to have your name blacklisted by that. It does seem most system have a very US focused design.
I still find it funny that even in my home country you can't use a lot of local special characters in names. Also most airlines won't accept it so technically I'm not giving them my true name!
Both versions work most of the time these days, but I still run into trouble once in a while no matter which name I use.