No, users on iOS 14.5 and above can still update to iOS 14.8, because Apple introduced a new mechanism called AlternateSU (Alternate Software Update) that allows OTA updates to 14.8 but not restores in iTunes/Finder, therefore blocking downgrades while still keeping 14.x supported for users who are not ready to update. But this also means that if your phone bootloops, you have no other choice than to update to iOS 15.
On iOS 14.4.2 and below, you can only update to iOS 15 as the AlternateSU mechanism didn't exist yet (unless you use the delayed software updates feature meant for enterprise managed devices, which works in a very similar way only allowing upgrades and not downgrades:
https://support.apple.com/guide/mdm/managing-software-updates-mdm02df57e2a/web)