This sounds interesting – that’s not how the front page in WordPress usually works. By default, all your latest posts will display unless you specifically set a certain page (not post) to act as your home page through Settings -> Reading.
It sounds as if your theme is doing something a little bit custom.
Having said that, there are still ways you can hide it. The easiest that comes to mind is editing your theme directly, but that isn’t recommended because your customisations will be overwritten if and when you update your theme.
So the better option would be to set up a child theme and then copy the file that is generating that category list into your child theme. It’s hard to say exactly which file it would be because it depends on how the theme is set up, but it could be in home.php, archive.php, index.php or even a separate file that is called by one of those files (you could look at the HTML source for something near the category list and search your theme files to find that).
Once you’ve located the code that is outputting the categories, you just need to modify it (in your child theme) so that if the category is equal to this one you don’t want to display, it skips it. I couldn’t give you the appropriate code for this without seeing how it’s written at the moment, so feel free to edit this code into your question if you’d like.
I realise this doesn’t 100% solve the problem for you yet, but I trust it gives you some direction in finding how to go about it! The problem is that it’s hard to know exactly how your theme has chosen to do this – and in the end, it might even be better to ask this of your theme’s creators.