Is there a way to restore the original system partition on an android device using adb or TWRP?

Question

Successfully rooted my grandfather's old Lenovo K6 Power to install kali nethunter for a project, but it was on android 6 and termux requires android 7+. i didnt realize this at the time and so I tried to update my software, but instead of rebooting and installing the new os, it booted into TWRP recovery, that i'd previously flashed to install magisk and what not. since the system upgrade from device settings didn't work i decided to flash a custom rom based on android 8.1 (LineageOS 15.1) so that i wouldn't have to update via official ota updates, and i wiped the phone to ensure a clean install, but i didn't think to take a backup since there wasn't any real data on the phone. i think i accidentally wiped the system partition along with everything else because now when i try to run 'df -t /dev/block/' the output is completely blank, unlike other working partitions. along with this, the LineageOS installer says it failed because it tried to mount the system partition to /system but there was no such partition (something along those lines). when i go to the reboot menu in TWRP it warns me that no OS is installed. do i flash a raw android 8 rom onto the device and install LineageOS on top of that?