because its rooted or system modified maybe not from you side, it might be because if the first owner if you bought it used and since then it voids the warranty and brake Knox from 0×0 (means official) to 0×1 (unofficial)
to check that out you need to to boot into download mode and this is how 1- turn the device off and then then press the power+ volume down+ bixby buttons for 9 seconds or around and it will boot into 2- second way ti to boot into recovery and from recovery there is an option to got to download mode power+ volume up+ bixby until Samsung logo appears after so you will get some options you need to press vol. up and down to go up and down you just press on reboot to bootloader or download using power button to click and when you boot to download mode you will be able to see what happend and you'll see the knox status if its 0×1 or 0×0 and how many time the software is modified
