Nightlife venue approaching can be done alone. I have done it. It's less than ideal to do it alone.
In nightlife venues, most women are out in groups with other women. Having a wingman helps in dealing with groups.
In a lot of daygame settings, the woman is already isolated from her group of friends. There's far less of a need for a wingman in daygame settings. I have seen plenty of women on walking paths with a friend. A wingman could help there.
Something I learned about nightlife venue approaching later is that groups of 3 are better for approaching when solo as compared to groups of 2. If a solo man approaches a group of 2, one female will be left out and alone. The dynamics are less than ideal. Approaching 2 women can be done solo in nightlife venues, but it's not the best. However, a group of 3 is better. In a 3 set, a solo man can connect well with one woman and the other 2 women in the group can socialize. There's no awkward social exclusion.
I prefer to do non-bar approaching (daygame) because it is less reliant upon a wingman. Additionally, it doesn't require late nights in the same way that nightlife venue approaching will require them.
It's difficult for most men to exclusively be daygamer approachers. There are some people in pickup communities that promote the idea of doing one form of game solely and getting good at that. With daygamers, the big challenge is interacting with enough quantity of women. This is less of a problem for nightgamers and online guys.