There are some discussions online about whether or not the Switch 2 will support switch 1 games in their docked profile but in handheld mode. For example, Metroid Prime runs on 1080p60 docked and 720p60 in handheld on Switch 1. On Switch 2, people are wondering if in handheld Metroid Prime could run in 1080p60 or it will be limited to 720p60.
Nintendo has not confirmed this one way or another yet. It may even be the case that in handheld the S2 would upscale the 720p image to 1080p instead of running it in 1080p native. We will have to wait and see how it all works
Yeah, it's less of a rumor/leak and more of an open question that Nintendo has yet to address. Either way, the bigger screen will be fantastic