mklink creates a symbolic link. Have you confirmed that it configured to point to the correct target?

Also:

• Check your debug.log in D:\Bitcoin. It will probably describe the problem in more details.
• Try opening cmd as admin and entering mklink again.

I tested this in Windows11 Bitcoin Core version 28.0, Regtest and it works without that error.
That setup works even if the directories are reversed.

Please tell if the symlink chainstate directory's contents are exactly the same as the original contents. (copied from the original chainstate)
Because otherwise, Bitcoin Core will surely show that message for having an empty/different chainstate.
If unsure, check your debug.log file for "[error] Fatal LevelDB error" lines.

I used "mklink /d ...." (symbolic link) on my successful test in Regtest.
But it's great that "/j" (directory junction) works on your case while '/d' didn't, perhaps it has something to do with the size of the chainstate folder.

I'm updating because after I moved the chainstate folder back & removed the mklink symbolic link I didn't face problems. I'm using my bitcoin wallet with blockchain & chainstate in the same SSD. If you're getting slow blockchain download I'll recommend using symbolic links because you'll save time.

The difference is subtle but you're right it's different. When I'd tried making a mklink symbolic link it failed. The junction link worked with out any problem. I couldn't understand why /j function worked but separating chainstate from blocks did help.