I can't recall any launches with only first-party games.
The N64 launched with only Nintendo titles, but it launched with only 2 titles, and was in some ways a fiasco. Some third party developers had got cold feet during the pre launch period and jumped ship to Sony.
Thankfully for them, one of those two titles (Mario 64) was mindblowing for the time (and still fun today), and it was worth getting the console just for that alone.
I don't know if new consoles could get away with that anymore though, since there's so many other options out there for games nowadays.
The N64 launched with only Nintendo titles, but it launched with only 2 titles, and was in some ways a fiasco. Some third party developers had got cold feet during the pre launch period and jumped ship to Sony.