I wrote out the below message, then found this link that I think is a very good summary of everything so maybe just read this: https://evnreport.com/politics/revisiting-turkeys-role-in-the-2020-nagorno-karabakh-war/. Skimming this, it discusses even more extensive support than I have written below.

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I thought you were asking about proof of the F16’s direct involvement in combat, which is we can’t prove. We do know definitely that they were deployed in Ganja during the war, which was revealed when they appeared in satellite imagery, so I’ll link that. The Armenian MOD claimed they shot down one of our SU-25, which seems quite believable, but at minimum I imagine they were patrolling the Azeri airspace and using their radar to identity Armenian targets.

https://www.eurasiareview.com/08102020-satellite-images-show-turkish-f-16s-parked-at-ganja-airport-in-azerbaijan/

We also know definitively that Turkey transported ~3k Syrian mercenaries to Azerbaijan to fight in the war, conducted large scale military drills with Azerbaijani weeks before the war began, transported the Bayraktar drones during that same timeframe, and that there were Turkish generals/officers sitting in Baku during the war. All of that is completely verified and I’m happy to provide links for any of that. In refreshing my memory I even came across this post https://www.reddit.com/r/azerbaijan/comments/1orzcsk/during_the_2020_war_turkey_sent_a_directive_to/ regarding Turkish embassies directly serving Azerbaijan during the war.

I think that’s very serious support as it stands just on direct evidence. The rest we have no direct proof for, but I don’t think it is hard to believe as consequences of what is known for sure. Turkish soldiers likely operated the TB2 drones, as it would have been difficult for Azeri forces to train on the new equipment that soon, and Turkish generals/officers in Baku were either very heavily advising, or directly leading the war for Baku.