Yes, to be honest it kind of fixed itself and I have no idea why it was not working before.
So my current setup is that dbt is connected to a github repo and you can delete branches manually in github and/or set up that branches are deleted on merge.
If you delete all the branches here and then go for “refresh git state” in the dbt frontend, the old branches will disappear.
It also turned out to be a non issue because we are not really using the dbt webfrontend for development because it’s pretty slow. Usually I just develop in visual studio code, created my branches there and push into the repo. Only some more testing is needed, I go to the dbt webfrotend, open my branch and test there.
Testing is also not optimal in the webfrontend from what I feel because there is no way to test on production data, only on your test clone which can take a good while to update.