Correct – see this presentation on alternative Android version naming.
All the official guides are linked off this page https://doc.e.foundation/devices/avicii . For nord there is no “Upgrade Android version” page, so you could fall back to the guidance we saw in the past for Android version upgrade
Caution: Do not install /e/OS on top of a higher version of stock OS. Before installing /e/OS ensure your device has the latest stock OS of the same version as /e/OS. If only lower versions of the stock are available then install the last available lower version before installing /e/OS.
Maybe /e/ documentation dropped this wording due to its complexity, but it will hold true in this case.
… yes … but R is not up to date (it is e-1.8.1) while S is 1.9. From this we can see the R build is being phased out in favour of S … so Android 12 ( = S) would be the better choice, see also from Development Updates
I see no specific guide to say that this will work.
… I see no need to go backwards – you are looking to advance Android version.
So you want to research X https://doc.e.foundation/pages/revert_oneplus_to_stock_on_windows X edit, no, that is the EDL recovery method, better https://community.oneplus.com/ or https://forum.xda-developers.com/t/oneplus-nord-rom-ota-oxygen-os-repo-of-oxygen-os-builds.4138085/ … where if you decide to go for e-1.9-s you will aim to revert to Manufacturer’s Stock Android 12 ( = S).