Restoring a userdir backup versus launching with --userdir: preserving NetBeans configuration after a failed upgrade

A failed Apache NetBeans core upgrade can leave the IDE unable to start while the user configuration directory remains intact. The goal is to restore project settings, keybindings, and plugin state quickly without reinstalling the operating system or losing customizations.

Two documented approaches exist: restoring an external filesystem backup of the userdir taken before the upgrade, or launching a working installation with the --userdir launcher option pointing to a previous configuration directory. However, NetBeans does not document a guaranteed automatic rollback or restore point for IDE upgrades, so recovery depends on external preparation. Reusing an upgraded userdir with an older installation can fail because newer configuration formats may not be readable by older releases, and plugin compatibility is not guaranteed across major versions. Behavior also differs between Apache NetBeans releases and between installer and archive distributions.

Given these constraints, which recovery path is safer when no pre-upgrade backup exists? Does launching with an alternate userdir avoid the format-compatibility risks of mixing userdir versions across installations? How can a user determine whether a specific NetBeans release documents any built-in upgrade rollback before relying on it?