Can middle name in Polish ID be a single letter ( Initial) for example: Anna K. Kowalska

Can middle name in Polish ID be a single letter ( Initial) for example: Anna K. Kowalska,
is such name is OK in official document Passport/ID?

That's an interesting question. I've personally never encountered this, though. On my Polish passport, my middle name is written in full and it only makes logical sense. A single letter is meaningless and I doubt an official would not challenge this before issuing a formal document.