a bunch, I keep like 3-6 games installed on my PS4 at all times. I don't worry about finishing/completing games, I just play what I feel like and uninstall it when I get bored/tired.
right now I'm playing COD vanguard multiplayer, dark souls remastered, GTAV, shadow of the colossus, and TLOU part 2 all at the same time
i'd say I play 1 game for a few hours before moving on the to next, daily, but I only game for like a few hours daily, so I'm not playing every game during my gaming time. I'll play some COD and TLOU, then the next day I'll play some GTA and Dark Souls, rinse and repeat, maybe just binge COD multiplayer for a week after that, maybe just focus on a single player game for a week after that week. I just do whatever I want, no point in worrying about a backlog when life is short and we're all l short on time anyways. that being said I don't buy too many games every year, maybe like 5 games max.