Hello, one of my unsold items has just been relisted automatically. I actually only wanted to make one attempt. Can I prevent this in the settings? Can I still cancel the item that was relisted unintentionally without any disadvantages?

As long as there are no bids on it, you can end it at any time.You can prevent that when listing it in the first place by being careful there. As far as I know, you can now only disable it in Seller Cockpit Pro by unticking the box when relisting.