I recently purchased a house. After moving in , I noticed that the previous owner has connected the floor drain directly to sewer and now sometimes its smell.
Are you sure it doesn't have a S or P bend under there? Since floor drains often only get water down them once in a blue moon there is a possibility there is a trap but it's dried out to the point it lets smells waft back up the pipe.
If it really doesn't have a trap and you aren't interested in installing one yourself the least effort option is to tape over the drain outlet until you get it fixed.
It's in German but when you scroll down you can switch to English (but at least on my mobile I only get to the Home page then and not to the product anymore)