In Episode 18 at 8:35, while Giorno and Mista were going to Venice, Fugo was in the car at first but then he isn't after the flashback? I reread this part in the manga but Fugo just seems to suddenly disappear there too. What happened to him? Did he split up somewhere to go with Bruno, Narancia, and Trish (I feel like I remember this to be the case...)? If so, could somebody provide the manga chapter and page where that happens?
Nope, there seems to be no explanation in the manga either, given the same thing happens. After the conclusion of Giorno vs Baby Face, both mention they are 1-2 hours from Venice. In the next chapter, they have arrived at the bridge leading directly to Venice, which then we can infer that a few hours have passed.
Note that previously, the entire team went in one car. Bucciarati, Abbachio, Trish, and Narancia are inside Coco Jumbo, and Fugo, Mista, and Giorno are sitting in the car with the turtle. The next chapter doesn't show Fugo OR the turtle, so it's safe to assume that within that two hour frame they had gotten off at some point.