Looks like to board a turkish airlines flight from Pakistan, a negative covid test is required. This is noteworthy and interesting because this rule isn't enforced by Turkey or Pakstani governments, rather Turkish Airlines itself. So the rule won't show up on Tiamatic or any consulate/embassies. I cannot find any official link on turkish website about it (will be likely updated soon), but the info below is credible if you talk to local turkish offices.

Are there other such restrictions from Turkish Airlines outstations other than Pakistan? Wouldn't want to be caught by surprise on these hidden airline-enforced rules (as opposed to govt imposed).

I know Emirates/Qatar etc have published a list of countries which require such tests for boarding, in addition to any govt rules which may or may not exist. Where is this country list for Turkish Airlines, surely Pakistan is not the only one uniquely penalized.