My taxtix 7 pro keeps asking me to “check o2” with a little plane on it.

Can you post a picture to make it easier to understand the issue?

Strange. I have never seen that. Garmin calls it "Pulse Ox" or SpO2, not only "O2". Do you have any third party watch faces/apps/widgets installed that might display this prompt?

Nothing new in the last30days. This atarted3-4 days

Altitude acclimation?

i really don’t  know and it’s very annoying

fsctory reset incoming inthink

The only other thing that hit me (and the plane icon may be relevant) is the Jet Lag Advisor?

Found it !!

https://forums.garmin.com/developer/connect-iq/f/discussion/328640/unidentified-message-popping-up-check-2-with-a-plane-logo

The message is probably "Check O2" and this is a function built in to the D2 series of watches (and also the Tactix, which also has the aviation functions). Because this is part of the core, built-in functionality of the D2 watches, this can't be turned off via Connect IQ. The user will have to turn of the Oxygen alert (or set it to some high altitude that will never be reached).

For reference, I own or have owned 4 or 5 different D2 models.

Ah so Ii infer from this that the altitude sensor is reporting the wrong altitudes?

Possibly.

One way to check is to go outside, load up the ABC widget and see what it gives you.

Then from the sensor menu, do a Calibrate by DEM for the altimeter