Lapsus is from latin. And yes, it could mean blunder. But apart from being Latin the word is used in the English language as well. So why would it be "likely from Russian"?

Because you can't talk about organized cybersecurity breaches of American corporations without someone blaming it on Russia because they drank the Kool Aid that only state-sponsored organizations have the skills to beat corporate cybersecurity drones.

Are there any other modern languages where the transliteration is literally "lapsus"? Genuine question.

I mean, doesn't prove anything. If they're smart they'd use the wrong language for their name. Or a double bluff...

Yep, in spanish you also say "lapsus". In school we mostly jokingly used it though.

Yes, in Italian we just use the latin word untranslated, as-is.

"Oh, that 2021 date on yesterday's email? Sorry that was a lapsus" (but in Italian)

Lapsus in German and Swedish.

Yup, for sure Serbian and Croatian.

French, too.

It's originally Latin, and hence borrowed into lots of European languages including English (lapse).

https://en.wiktionary.org/wiki/lapsus#Latin