3 ms·

It's just an internet meme phrase. "X is not a serious Y" just means that X is a joke. It's a dumb phrase and overused in contexts like this.

• pfdietz 1mo ago
  "Is not serious" is not serious?
• antonvs 1mo ago
  That’s not the meaning here. It means that Microsoft lacks the qualities required to be taken seriously, like competence or reliability.