I'm from Ireland, an English-speaking country in Western Europe. I have a name that is a typical Western name. In theory, I should be the happy path for any name system.
But even I don't have one canonical full name. Even with just the government, the name on my birth certificate, passport, and tax documents is different.
Name 1: I was named by my parents after a friend of theirs. That friend commonly went by a short version of the name (think "Jessie" vs "Jessica", though that's not the real example). Anyway, since I was born in Ireland in the 90s, my parents had me baptised by the Catholic Church, which expected you to name your kids after saints. In the form which the saints used. This was less about any strong faith on their behalf, and more of the fact that it made it easier to get into any of the 90% of schools run by the Catholic Church. I think even then, it depended a little on which priest you were dealing with as to how strict they were with the name rules.
But anyway, the extended, "saint's" form of my name was needed for the baptism, so my parent's put it on the birth cert, plus a middle name. They (and consequently I) never used the extended version of my name, but my birth cert reads "ExtendedFirst Middle Last"
Name 2: Anyway, then my teenage years came and I went abroad and I filled out a passport application form to get one for that. It had fields for first name, middle name, and last name. So I put in the first name I actually use, dutifully filled out the middle name field even though I never use that, and then put in my last name. So my passport has "First Middle Last".
Name 3: Then when I came to actually paying tax as an adult, I had to provide details to the tax office and my first employer that lined up. At this point my middle name was well and truly out of use, so both got just "First Last". This is also the form of my name that appears on most utility bills, professional correspondence, etc.
Name 4: And then on top of that, I have a nickname I'm commonly known by. This is what's on a lot of personal correspondence (sometimes as just Nickname, sometimes as Nickname LastName), what people call me face to face, etc.
Now a lot of countries have a concept of a singular "legal name". In some countries it may be at least procedurally incorrect or sometimes even legally fraud if you were to use something else in passport applications, tax documents, etc. But Ireland does not. If you use something as your name, it is your name. Most government interactions will accept evidence (such as utility bills, employment contracts, etc.) that you've been using it for 6 months to update the above documents.
For any of the 4 variations above, I could provide enough evidence to the government to get them to update the other documents in line, but it's just not important. But if I was to bother I'd use "First Last" as the target name, and I'd actually rather not update the passport as I travel to the US frequently enough and "your name is different to last time you were here" strikes me as the kind of thing to make US immigration unhappy.
Alternatively, you can register a deed poll to get a piece of government paper stating effectively "X Y Z has informed the government they're now known as A B". But this is not a prerequisite to changing your name, just a way of short circuiting the process if you're stuck getting documentary evidence that you have changed your name via other mechanisms.
And that's all before we get into marriages, gender transitions, Irish vs English names, immigrants who anglicise their names, confirmation names, etc.