No, it's not; 9/11 was the only event that has led to invocation of the mutual defense commitments under Article 5.
It has, however, gotten involved in other conflicts, both in response to UN calls and as a result of regional security consultations under Article 4. These include, most notably, Libya beginning 2011, Kosovo beginning in 1999, and Bosnia beginning in 1992,
False. NATO Command led the bombing of Libya in 2011 (taking over from the French).
https://en.wikipedia.org/wiki/Operation_Unified_Protector
You can search for "NATO Libya Lessons" and get a ton of articles by analysts, many published in US military journals and/or written by US think tanks on the subject. For example, here's one from RAND:
https://www.rand.org/pubs/commentary/2014/11/natos-campaign-...
[1] https://en.wikipedia.org/wiki/NATO_bombing_of_Yugoslavia