the frrmware version in my forerunner 945 is 7.10 but on garmin connect the version is 2.80 ;) why ?

That is only the map version. Not the firmware.
What? I understood that you were telling 2.80 is a map version, which is isn't. That 2.80 points to firmware, but it's the version shown for some reason during roll-outs if you are not part of getting the firmware yet.