The Bug:
You cannot select incompatible resource packs within the resource packs menu via keyboard navigation.
You are able to select incompatible resource packs via the mouse cursor but not via keyboard navigation, therefore introducing an inconsistency.
Steps to Reproduce:
Navigate to the resource packs menu.
Attempt to select an incompatible resource pack via the mouse cursor and take note of how you're able to, but are prompted with a warning.
Attempt to select an incompatible resource pack via keyboard navigation.
Take note of how nothing happens.
Observed Behavior:
You are able to select incompatible resource packs via the mouse cursor but not via keyboard navigation.
Expected Behavior:
You would be able to select incompatible resource packs via keyboard navigation.
Okay, so, there's some confusion here I'd like to clear up. You can indeed use space/enter to select resource packs within the resource pack menu, contradictory to what this report currently states. This was a change specifically stated within the 23w03a article.
However, incompatible resource packs cannot be selected via keyboard navigation which is an issue since you can select these using the mouse cursor. I think this was what the reporter was trying to describe in the first place. With this being said, I've updated this ticket to appropriately reflect exactly what the problem is here.