I have a Portable Seagate 1TB HDD with some files around 200Gb in it. Can i use the same as a backup location for Timeshaft? Or make a new partition in my laptop HDD and set that as backup location. I dont have much of personal files in my laptop but i want to use timeshaft for the os & configurations. Recently, I did somthing dumb and had to install LL 3.8 from the beginning. I dont want to happen that again. Please Help.

Timeshift is default in LL4.x in LL3.x its Systemback.. Yes will snapshot the OS for recovery - I don't recall but I assume you can to external..
I'll check my LL3.x box in a bit
If using Sysetmback - you'll want to make sure the disk/partition is formatted Linux usable (non NTFS preferably EXT4) **If you have data dont reformat it, you will erase..
There are some issues with symbolic links if across disks - sometimes systemback will error/fail (excluding those dirs usually works - mine were in my home - saving to my NAS)..