Thank you Behdad for your quick reply. Two years ago, when we discussed the issue, I had a OnePlus 5 and I was able to see the character. At the time, my friends who did not have pure Android on their phones could not see the character. Recently, I went back to see if I could find a way to type a character on my Samsung phone. Nothing worked though.
Just now, I went back to our conversation two years ago and I realized that I had missed one step: adding Farsi on Settings/Languages. I am now able to see the character by long pressing 0 on GBoard.
This is exactly where users on Samsung need to add Farsi: Settings/General management/Language and input/Language.
This is awesome! Thank you Shervin for your suggestions. I tried side-loading GBoard. It did not work for me so I uninstalled it and installed Gboard from the Play Store again. It would be good if someone else tries just installing GBoard and adding Farsi as a Language to see if it works.
Thank you all,