Welcome to the community @nullentry
I see why you may need to use --standalone but it is harder to debug.
First, are you sure your ISP allows port 80 connections to you? It looks to be a Vodafone IP and if residential sometimes ISP don't allow port 80 (HTTP).
But, for now let's assume it should work. Can you try this command
sudo certbot certonly --standalone -d files.soxd.hu --debug-challenges -v
This will show you a URL and then ask to press enter. Do NOT press enter. Just leave it paused like that and let us know when it is ready. Or, while it is paused try to reach your domain using http://files.soxd.hu from outside your local network. Like using a mobile phone with wifi disabled to use the carrier's network.
You should be able to get some response from Certbot using --debug-challenges while it is paused.
If you get a timeout you will need to inspect each part of your local network to see where it may be blocked. And, contact your ISP about port 80.