Applied resource/behavior packs in the new version of the "Create World" screen do not have any option to change their subpacks(resolutions), even if those subpacks are defined in the manifest correctly and can still be changed via the "Edit World" screen which wasn't updated yet.
"Create World" screen:
[media]"Edit World" screen:
[media]
very nice of mojang to forget about their own game features with their Ui changes, subpacks are utilized by many resource packs out there seeing new ui rolled out in newest release without this issue addressed is really something to think about