Your final comment about blank categories you can do already.
Go to Tools -→Categories-→New Create a new Category, back space the offered Category name out & leave it blank, click OK.
Now you will have a blank orange diamond category at the top of the list. To make it the default
Highlight an account in the side bar, then Go to Accounts-→ Edit Account, change the default category to your new blank one.
Having said that, it’s probably not a good idea to have lots of blank entries as it rather screws up any reports you may want to run. But it does allow you to do quick manual entries & go back later to change the category to something more appropriate at your leisure.
I did some testing with a blank category name some years ago. I found it problematic Moneydance did not always work well with such a category. I ended up creating a category called 'Uncategorized' and I set it to be the default category for each account.
As Moneydance is based on account rules transactions are required to have two sides. by having a default category that requirement is always met as the category provides the other side of the transaction.