Game Room VS Retroarch + core emulator Questions

[Goldensun7]

Hello community! How are you all doing? I'm new to this console and I have a few questions. What's the difference between playing games from Game Rooms or from Retroarch Games? It might be a silly question, but for someone new to this world, it's not clear. I also noticed that if I open games from RA (Retroarch), it gives us the possibility to change the simulator core and choose one from the list, like Gpsp, in addition to vbam and mgba. What's the difference between emulators and which do you recommend? If you could clarify doubts or explain the purpose of each one, I would appreciate it. I've seen a video on YouTube where they say that for Pokémon, the best one is Gpsp because you can speed up the game just by pressing R2... or other conveniences, I don't know how to fast forward in Mgba... but I'd like to know which one is better in terms of performance as well.

Lastly, How can I change RTC/time so In pokémon Games I can easily change time night/dusk/day

Well, thanks for everything to those who can help me out!!

Cheers