Hey,
I am not a great dev in C#, so I paid Game Creator on Unity for my project; this is a visual scripting tool.
I use it to create prototypes, and project it helps me a lot instead of learning complete programming.

Could that type of tool be okay, If I am solo?

Does it create asset files that can be used stand-alone (or at least come with a runtime library you are allowed to pass on to others)? Then it should be fine, just remember to remove it from any source uploads.
OTOH if you can't provide a copy of the project that doesn't include that tool and still be working, then I would say it's not ok to use.
(Also, if there's a paid tool that also has a free "lite" or demo version that could be used instead (but maybe just read-only and not for further editing of those parts of the project), it might be ok, but would make further tinkering with your game for others to learn from needlessly difficult...)

If you rely on Visual Scripting, have you looked into Unity's own rendition of it?