The steam achievement "seal the deal" sets a goal of acquiring a triumph seal in game in order to earn the achievement as described on the achievements page for destiny 2 on steam. I have uploaded a screencap of this. So I went to great effort in order to unlock this achievement. I spent tens of hour over multiple days in order to unlock the deadeye triumph seal. Unfortunately it did not unlock the achievement, and upon further research I found in a deleted article on your help page that the achievement is for a few select triumph seals. The only currently available titles that would unlock the achievement would be Dredgen, Unbroken, Cursebreaker or Rivensbane. All of these require the forsaken dlc. My suggestion, because of how this wasted my and others' time, would be to either clarify that the achievement is for specific titles or to make the achievement function for all titles as described on the achievement itself.