Is there any standalone QA settings (RegEx) editor in Studio, without having to open a project, then the project settings?
I would like to be able to work on my RegEx settings without being in any project.

You are currently working on UAT
Is there any standalone QA settings (RegEx) editor in Studio, without having to open a project, then the project settings?
I would like to be able to work on my RegEx settings without being in any project.

Is there any standalone QA settings (RegEx) editor in Studio, without having to open a project, then the project settings?
There is not such a Regex Editor.
What I do is opening the Sample project and work there, maybe importing regex rules, and when done, export the regex rules to be imported where I need them.
Yes, it's what I do too. I can also do it in the Options, under the File menu, but it is less straightforward than a directly accessible dedicated editor.