I had this same issue with not being able to access my QS Nexus quests and only decals in the QS store, but I fixed it today!
I usually play from the Xbox app on PC, but I noticed that my Steam version of No Man’s Sky said “Connected to Discovery Services”, whereas when I launched the game from the Xbox app it was constantly connecting to Discovery Services.
I went onto the Microsoft Store and in the top right corner, hit “Downloads and Updates”. Then again in the top right I selected “Get Updates”. It downloaded all available updates for the store, including Gaming Services and Xbox app, etc. Then after everything was finished updating, I opened No Man’s Sky in the Microsoft Store and it had an update that I had no idea about (it was about 1000 Mb total).
Then I opened the game on Xbox app and it said Connected to Discovery Services and all of the QS Nexus quests and items in the QS store were available! I hope this helps someone 