Apple Watch 4 blood pressure

As far as I know the Apple Watch 4 currently does not measure blood pressure. There are some non-Apple apps out there that claim to show BP but they actually just sync to some other device -- they don't use the Apple Watch to measure BP.

I think you're just repeating what I already said i.e. the Apple Watch, itself, does not currently (version 4 running Watch OS 5) measure blood pressure. AFAIK blood pressure measurement isn't a feature that is anticipated in Watch OS 6 either.

I used an Omran BP monitor for around 6 months that would sync the readings to my iPhone by bluetooth. The readings would sync with the Omran iOS app which was then shared with Apple's Health app. However something went wrong when they updated their app and I lost all those previous readings in both Omrons app as well as the Health app. I was under the impression they readings were being saved in the Health app when the 2 syncing together. I no longer use the bluetooth connection and opt to manually enter the readings directly into the Health app where they are backed up regularly.