Greetings!
The "Seal the Deal" achievement doesn't pop with newer titles. You'll have to complete a Forsaken era seal, and those are:
- Unbroken
- Dredgen
- Rivensbane
- Cursebreaker
You could easily get Cursebreaker. At most, this’ll take you 6 weeks on account of the ascendant challenge rotation - this if for the emblem and remaining bones / eggs.
Just a heads up, Keep of Honed Edges ascendant challenge sometimes doesn’t track and needs you to take the relic sword through the portal after opening the chest. Doing the time trials makes tracking ascendant challenges easier as each has it’s own triumph.