I have a Garmin 55 in each of my two cars and I don't have this warning message. Ergo, my Garmins go into video recording after starting the car when power is applied to the Garmins without any intervention. Possibly the basic settings are corresponding or there could also be a fault in the car's power supply. It would be interesting to know what kind of warning message it is.
Greetings
"With the Garmin dashcam, you also have to click away a security notice every time you switch it on - annoying", says the test report from Heise (https://www.heise.de/select... and the overview: https://www.heise.de/select...). What firmware do your dashcams have? (Heise: V 3.70) . Perhaps they have adapted this in a more recent firmware ...