yogeslegend - Welcome to Legend!
The syntax for no tag is: -is:tag
You can also trigger this from the basic filter dropdown.
Under the “Contains” section, click the hash tag once - it turns blue and shows you all items with a tag. DOUBLE click it however, it will turn RED and show you all items without a tag.
Another option that may fit the use case you describe: create a pane that is focused on your inbox and grouped by tag, there will be a section at the bottom that is “No Tag”. You can collapse the other tag groups to see only “No tag”. Or, you can leave them open, and drag items between the sections.