Most of the Switch 1 games probably won't get a (free or paid) upgrade or reolution-patch from their developers... some third party developers might not even exist anymore to patch their Switch 1 game.

So in which mode the Switch 2 will play them, when that new console is undocked?

As far as I know, Nintendo hasn't positioned itself for these cases. (Please correct me, if I'm wrong)

There are four possibilities for these unpatched Switch 1 games:

• Switch 2 undocked will play all unpatched SW1-games with SW1-undocked settings (720p or even below)
• Switch 2 undocked will play all unpatched SW1-games with SW1-docked settings (better suited for the 1080p-display)
• SW1-undocked settings will be the default for better battery life, but you can active a boost mode for SW1-docked settings
• SW1-docked settings will be the default for better image quality/performance, but you can active a battery mode for SW1-undocked settings

Nintendo should make it possible to run switch 1 games as if you were docked on unpatched titles. But I have a suspicion that's not going to be a feature.

I voted 2 because it seems obvious, but I guess it'll depend on how, exactly, the translator layer emulation handles Switch 1 games. It could just be docked for docked and undocked for undocked, which would be a very Nintendo thing to do.

Nothing has been revealed yet on this front.
But running Switch 1 games in docked mode on a Switch 2 handheld would be amazing.

Yeah, option 2 seems most reasonable, given the jump in power.
Then again, seems that, at least for now, that backward compatibility is not that great to start with, which, honestly, is not what I've expected, being it's nVidia SoC in both consoles.

I expect both NS1 handheld and dock modes to just increase their NS2 performance respectively to their top DRS/FPS.
But as it is not hardware emulated this time around, the JIT compilation could be able to have the docked NS1 experience portably.