The "Check for updates" sub-menu in the LabVIEW 2019 "Help" menu starts the "NI Update Service" which doesn't find any update.
This is strange since LV 2019 is installed through NIPM. NIPM does show an update for LV 2019, LV 2019 SP1.
The sub-menu should've started NIPM to check for updates to LV 2019 instead of "NI Update Service".
Hope this can be fixed in LV 2020.
Thanks for flagging this up to us!
LabVIEW 2019 SP1 is an separate package from LabVIEW 2019. Therefore, this would be considered an upgrade rather than an update. However, you're absolutely correct to expect that NIPM should be started rather than NI Update Service.
If you'd like to report this as an official bug, you can create a Service Request ticket with Technical Support here.
The Technical Support Engineers will likely need some additional information in order to replicate your set-up and confirm whether this is definitely a bug.