adb device doesn't listed on cmd {Lenovo K8 Plus}
Common mistake these days people do not read the instructions.
Here is a example Warning from TWRP site:

This device uses dm-verity!
This means that swiping to allow system modifications will prevent you from being able to boot if you are using the stock kernel. In order to bypass dm-verity's boot prevention, you will have to install a kernel that has dm-verity disabled in the fstab.

Go back to the Tutorial where you have downloaded TWRP and read, i am pretty sure there is something you forgot to flash.
Universal DM-Verity ForceEncrypt Disk Quota Disabler
Another common mistake after flashing TWRP you must not boot into android. Reboot straightforward into recovery right after flashing, otherwise your custom recovery will be replaced with stock recovery
/system/recovery-from-boot.p