The Rivian R1T Owner's Guide contains everything you need to know about operating your R1T. This guide includes information on access, climate, Bluetooth capabilities, vehicle operations, charging and other features.
rivian.com
Search for "Status Indicators". Page 91 in the online guide, but you can also search the manual on your center console.
The yellow car symbol means Forward Collision Warning is malfunctioning, the Red triangle I believe always shows up if you have any abnormal warning lights like this.
This could be a real warning or not. I would try a soft reboot - look for "RESTART THE SOFTWARE" in the manual, page 234 online, and see if that fixes things. If not, try a hard reboot - look for "RESTART THE VEHICLE" in the manual. That will take a few minutes. If you are still getting the warning about the FCW system after both of these I would contact Rivian.