Why was I perma banned from the Sea Of Thieves insider?

You'd need to contact the Developers of Sea of Thieves to ask them why...however, the most likely cause of a perma-ban would be violation of the Non-Disclosure Agreement you agreed to when you signed up which prohibits discussion of any insider features outside of Official SOT Insider Channels.

Not saying you did that of course, just that it's the most likely reason. There are other reasons why:

"What happens to Insiders that break their NDA?
Any Insiders found breaking the NDA will be removed from the programme.

Do not take photos, videos, or audio recordings of the Game.
Do not post photos, videos, or audio recordings of the Game on any venue. This also includes the Insider Forum.
Do not describe any part of the Game on any venue unless we’ve instructed you to.
Do not allow others to watch you play the Game.
Do not leave the Game running unattended."

https://support.seaofthieves.com/hc/en-gb/articles/360018595374-Insider-Programme-FAQ

https://support.seaofthieves.com/hc/en-gb

Sorry because this is not the right place to ask this but: how can i open a thread asking my problem? I dont see the "button" to open threads.

at the top of the page, click ask a question.

Sea of Thieves Insider is not related to the xbox Insider. Just go to the sea of thieves website to register for the Insider program.

i should have re written and specified i signed up for the Sea of Thieves Insider Program, but i own the game as a disc and so i have to get the Insider Build from the Xbox Insider Hub

After uninstalling and reinstalling Sea of Thieves and the Xbox Game Bar many times, I am able to invite and accept invites on Sea of Thieves Insider through the Game Bar. I am able to send invites from the Game Bar for Sea of Thieves. However, when I receive an invite or try to join in on Sea of Thieves, I still have the same problem. Sea of Thieves and Sea of Thieves Insider are two different builds. There must be a file somewhere on my computer that is not being deleted or uninstalled and it's not allowing me to accept these invites on just Sea of Thieves. I don't know how to find this file.