I researched some more and it looks like my HDD uses some technology which I wasn’t yet aware of.
So the HDD that’s there on my laptop uses Shingled Magnetic Recording. I am not geek enough to completely understand this thing, but what I understood is that it has denser data blocks. Writing data to a track requires the data on adjacent tracks to be re-written too, making the writes slower. A concern for people like me who write lot of data.
These types of HDD need trimming. And so lsblk and fstrim reported trim support on my HDD.
The general image of these HDD on the internet doesn’t look too good. In my case, the product listing on Amazon didn’t mention any such thing. Even on the Dell website, it doesn’t say that my HDD is SMR.
https://www.reddit.com/r/DataHoarder/comments/57eosc/smr_drives_aka_archive_drives_a_word_of_caution/
From Wikipedia
Western Digital, Toshiba and Seagate have sold SMR drives without labeling them as such, generating a large controversy, as SMR drives are much slower in some circumstances than PMR drives.[13] These practices were used in both data storage-dedicated (for servers, NASes and cold storage) and consumer-centric HDDs.
Edit: So I’ll enable the fstrim.timer and let it trim my hdd partition too, as it was doing earlier. Thanks everyone for your time.