Is there a forum ban on inserting links in created topics?
I really have not seen such here. I believe you too have observed it yourself. Possibly it is not allowed here as you can see for yourself that majority of the topics here have no such features and as such are not clickable to redirect you to another page outside that of the platforms. You could try it yourself if you can but doing such, you should know that you are liable for your own actions.
It's fine, there's no ban too, the chance is only your post could be deleted by moderator, that's all.
I thought as much because I have actually not come across any topic here with a clickable link to redirect you out of the platform. What I am very sure of is post content which can be embedded but not topic. But however since it is not an offence against the platform, then it seems OP can try it out but I hope the link would not be something not in line with the principles of the platform otherwise it would likely be deleted as you have said.