Cannot use !Tag when searching for multiple scoreboard tags.

I've searched the web and found no mention of whether or not using ! to find entities without a tag works. I find it very strange that it works within the @e selector, but not in the curly brackets. I've tested it quite a bit and believe I have not missed anything major (Other than if it's supposed to work in the first place)

I've found that using
/scoreboard players tag @a add Test {Tags:["!Test"]}
Does not work but using
/scoreboard players tag @a[tag=!Test] add Test
does.

Obviously, this is an example that uses only one tag, but it is very much needed to have multiple !s in one of the projects I'm working on and I wish to know if it's something I will have to work around or not,

I've also tested the following commands, and both works, so that means that my syntax is not incorrect.
/scoreboard players tag @a add Test
/scoreboard players tag @a remove Test {Tags:["Test"]}

Thank you