When a plugin can't auto-update because another plugin pins it to a specific version, users now receive a clear notification explaining the hold: "Autoupdate held". The notification identifies which plugin is blocking the update and whether those pinning plugins are disabled.
Evidence
Autoupdate blocked notification type (search for "autoupdate-blocked-by-pinner" and "Autoupdate held").
Strings lifted out of the shipped bundle, so the claim above can be checked against them.