This website explains what the limitations of a retail mode phone are and how to minimize the annoyance of the built-in retail mode app.
#1) They can NEVER be used to make phone calls and cannot use Data Plans and can only connect to WiFi networks.
#2) The retail mode app uses up 52GB of the onboard storage. Adding a large microUSB card is a good idea.
https://forum.xda-developers.com/t/lm-g710v-the-lg-g7-thinq-retail-mode-demo-mode-thread.3910502/