I'm so ready to be disappointed to hear the backwards compatible games will run exactly the same as on the Switch.
that's gonna be almost impossible to do.
this isn't the same situation the Wii or the Wii U were in, the latter of which hardware emulated the previous system by going into a completely different hardware mode and OS environment, while the former used nearly the exact same hardware and just had to slightly adjust clock speeds.
the Switch 2's GPU can't just change into Switch 1 mode for example and just turn off 1280 cuda cores and completely change its CPU clock speed every time you launch a Switch 1 game.
the Switch 2 OS for example still need to work like always, and it will expect a certain hardware that is allocated to it with a certain clock speed and a certain amount of GPU and CPU resources.
the Wii U didn't have to do that as it completely switched into the Wii OS when playing back compat games.
even the PS4 Pro for example was able to easily emulate a base PS4 for games where it was necessary, as it was designed specifically in a way that makes this doable seamlessly. it had exactly 2 times the GPU hardware on board, with basically a mirrored set of GPU cores stuck to the original PS4 GPU cores. and the OS was also designed for the base PS4 hardware so it wasn't an issue in that department either if it slightly altered its clock speed.
so with what we know about the Switch 2 APU, it's almost impossible for Nintendo to give it a hardware mode that limits Switch 1 games to their original performance. the GPU is a completely new one, and can not be easily split into sections to emulate a Switch 1.