Let's say we put third party games into 3 categories: 1) Games not coming to Switch, 2) Switch exclusives, 3) multiplatform games.
Switch exclusives are mostly going to come from Japan. There might also be some indie games that are either Switch exclusives or timed exclusives since it is going to be the platform with the highest install base.
Multiplatform games are going to be almost all of the other games coming from Japan. Going forward 90%+ of Japanese games will either be multiplatform or Switch exclusive. The few that aren't are going to be the ones with very high end graphics like Final Fantasy or Resident Evil. But there are other games that might be considered AAA (like Persona or Dragon Quest) that really should be coming to Switch unless Sony gives them a special deal. Lots of indies will be multiplat. Some Western games will be multiplat. (I'll try to explain more below.)
The games not coming to Switch has very little to do with graphics or the Switch's power or whatever. It has more to do with the business model of the largest Western Publishers (EA and Activision especially, but also Take Two and Ubisoft as well). One strategy for businesses in general is to create barriers for smaller competing firms. In gaming this means having a big budget game, especially when it comes to graphics. So a company like EA does not want Nintendo platforms to do well. It's against their business model. Not only do they have to compete against Nintendo first party games, but they really don't want to compete against a bunch of small and mid budget games. EA does not want a level playing field, and that is actually what the Switch provides these smaller developers.
So, there will probably be a lot of PS4/5 cross-gen games (and same for XBox), that will not come to Switch. These will be from the bigger Western publishers. But when it comes to Japanese games and small/medium Western games, then I'd expect a whole lot of multiplatform releases for as long as the Switch is a viable platform. The big Western publishers will probably make the transition to PS5 about as fast as they did going from PS3 to PS4 a generation ago. All of those other third party games will end up on Switch.
I'm not sure how long these same types of games will get released on PS4 and XB1 though. Hardware sales are tanking fast for these systems. I'd expect software sales to decline in the next couple of years too. I wouldn't be surprised if in 2023-2025 we see quite a few Switch/PS5/X|S releases.