These setups are a bit complicated and everyone has different ideas for their home security, so you might need to do a little experimentation.
When you setup SHM you tell SHM which Motion sensors and door/window sensors you want to use to trigger an alarm and trigger an intrusion alert in the AWAY and.Home Modes if I remember correctly.
In my case I do not want any outside sensors or cameras to activate SHM ant trigger an alert, so I do not use them in SHM. Let me give you a couple of examples.
If my storm door is opened, I want a notification and I want the outside Arlo camera pointing at my door to start recording in the AWAY mode. No Alarm, but if my front door is opened I want SHM to do its thing and fire off an alert, (I am using an ST multipurpose sensor on the storm door). I also have an ST motion detector mounted outside above the storm door to also alert me if someone is dropping off a package or the mail has arrived, or some salesman showed up on my front porch. I do not want to set off the alarm, but I do want a notification and a vider of who is there.
If someone tries to crawl through my windows I want the outside sensors/cameras to pick that up record it and notify me. Then again I want SHM to fire off using my indoor motion sensors and cameras. At this point, I want video only from the camera in the room where the activity is happening.
I only arm my system using Routines and I have custom rules for each device to turn on lights and whatever else.
Hope that helped,
Brian