There's been some recent discussions (again) about QSOs using WSPR. Certainly possible if you run WSJT7 but why bother?
The conventional criteria of what constitutes a QSO is the "intentional exchange of information" including call signs and signal reports. The key word being "intentional".
WSPR, in my not-so-humble opinion, meets that criteria. I put a signal on the air including my callsign, maidenhead location and power output with the intent that someone, somewhere will spot me. I monitor the WSPR segment of the band I'm using with the intent of receiving other stations whose intent is the same as mine.
If I spot you and you spot me within a reasonable time frame then we have intentionally exchanged information... call signs, signal reports, locations and power levels. If I spot you and you spot me within the same 10-15 minute time frame that constitutes a valid QSO in my book.
It could be argued that one of the transmissions in the exchange must contain both callsigns. If that be the case then 99% of DXpedition pileup or contest QSOs do NOT meet the criteria of being a valid QSO... yet they are still accepted as valid for QSLs and awards.
It all depends, I suppose, on how each person defines what a QSO is. For me, I don't worry much about it since by my definition I have many FB QSOs every day using WSPR. I look forward to seeing the same callsigns each day and welcome the new ones that keep popping up.
73 es GUD DX TU de NH7SR
'Bear'