Sort of, though Wii and Wii U are a bit more complicated than that so this somewhat of an oversimplification. The ELI5 answer is that some hardware components are directly upgraded and can run in a compatibility mode, other components are just the original hardware thrown in separately.

New3DS is the most recent and most notable exception. It's directly upgraded 3DS hardware, but the CPU downclocks to run at 3DS specs on all legacy titles (and there are almost no native New3DS games so this upgrade was pretty pointless). Softmodding can unlock the full clockspeed, and most games do work fine this way but there are a few rare bugs.

I expect Switch 2 will just be the same architecture upgraded, because that's a lot easier to do now, while the old style of true redundancy would inflate costs too much today. It's also worth noting that Switch titles already expect variable performance in order to support handheld and docked modes, so I doubt much would break if allowed to overclock. But I could also see Nintendo not even trying to support it if even one bug might exist somewhere.

[–] vaguerant@fedia.io 2 points 1 day ago

Just adding on to this, I do think the "up-specced OG hardware" approach something Nintendo has done before. Upgrades like GC to Wii and Game Boy to Game Boy Color are really just boosts to the clock speeds and RAM, they don't have anything specifically included for BC reasons (unless you're counting GameCube memory card slots). They really are just iterations on the same hardware. Similar to the New 3DS, on modded consoles you can run GameCube games at Wii clock speeds and they almost all work without issue.

On that subject, the fact that Nintendo says the compatibility won't be 100% is potentially encouraging. If the Switch 2 was just going to downclock compatible parts to their Switch 1 performance and was otherwise identical, you'd expect all games to work. The reduction in compatibility could be because games are going to be running with Switch 2 clocks across the board, which most games should handle just fine and a small handful may not.