You don't need yellow quests to finish soulboost. This has been discussed for five months now with every other person raising it as a "new" "unsolved" issue. It's not. I've done it on multiple characters that had finished story before soulboost became a thing. Do other quests, later stages will unlock after sufficient login days have been achieved. Move on. We've all done it.
And to address your future complaints you're not yet aware of:
1) Yes, 3 dungeons in stage 2 are not in F8 anymore, BUT they still exist in the world, it just means you'll have to enter them on the actual world map. Hundreds are doing the same thing right now. Move on.
2) Yes, you actually can't finish several quests on page 4 due to Hall of Trials no longer being demonsbane, no, you don't need them. There are equivalent quests in Grim Nexus that didn't exist when soulboost was first released. They were added for you, to be able to get the same amount of points I had available when soulboost was new. You are not missing any points, you are in the same situation everyone else was before Grim Nexus update. Just ignore the impossible quest, consider its presence a visual bug.
There, saved you some future forum posting.
You're welcome.