@Staudey Ok, Turned out I needed to copy the include
header folders too. I didn't know about the discussion to finally include it in the repos. I know Joshua had openly spoke about his dislike towards libhandy multiple times on this forum and on blog post. It is good to know libhandy is finally getting included, because a lot of apps are now depending on it. Moreover, when I tried to install these apps with flatpak, they still didn't ran because of missing libhandy from system.
I personally hate snaps and flatpaks. So if an app in unavailable in repos and doesn't provide appimage, I prefer to build them from source directly.
Q: When it is officially included, will it cause any kind of conflicts or issues because of the files I manually copied?
@ReillyBrogan Thanks for solution, I was missing the include folder. I learned something new because of this. I also now have a better understanding about difference between normal package and -devel packages. I would have waited for libhandy to be officially included if I had known about it. At this point, there are just too many manual copy, pasting, symlinking, for me to go back. I just hope that when It syncs, it won't break my system.