Hi hope your doing well..i came accross this and i wanted to help you get troubleshooting to see if device has been rooted
Step 1: On Samsung devices there is a status that samsung implements to dwtect if root was implemented evwn when unrooted to do this go to
"Settings>About Phone>Status" and scroll down to the oprion that says
"Device Status" if it says
"OFFICIAL" then the phone was not tampered with in any form of way, but if it says
"CUSTOM" this means the device has been altered in some form or fashion and will not recieve any system updates
Step 2: you can ensure if you have root as well by downloading this app for samsung devices this can also tell you if your device has root access
https://play.google.com/store/apps/details?id=org.vndnguyen.phoneinfo
Step 3: if your phone was tampered with you can reflash the firmware back to stock using odin and i can asist you in that if you like
P.S to ever want to enable developer options samsung never has this enabled by default go to
"Settings>About Phone>Build number" and tap it 5 times, if it does show as shown it in a tab named "Software Information"
Hope this helps