I made a transfer from my Savings Account (Budget) to my Investments Account (Tracking) of 6k however, now it is showing that I still have the full amount on my Savings and -6k on my Investments account.
What am I doing wrong?
You seem to be confusing accounts and categories. Accounts tell you where your money is. Categories tell you what the money is for.
Your screenshot shows categories, not accounts. When money leaves your budget, whether through spending or a transfer to a tracking account, it gets assigned an expense. In both cases, you also need to have money available in the category for the transaction or your category goes overspent.
In this case, I think you would need to move 6000 from the Savings Account category to the Mutual Funds category.
And for future reference, savings account isn't really a job. Sending money to an investment account is.