Syncthing’s web GUI is only reachable from localhost by default. In your case localhost probably means the Ubuntu VM. It appears you’re trying to reach the GUI from the outside, which is not possible in the standard configuration.
You need to either access the GUI from within the VM or configure the GUI listen address to listen for external connections. The guide you linked actually covers how to this.
In short, changing the GUI address can be done either
By changing the config via the GUI (which is sort of a bootstrapping problem, because you need to access the GUI for that)
By modifying config.xml
Or by setting the -gui-address command line parameter (this is explained in the guide)
It took two seconds of skimming your log to see these lines:
Feb 18 15:17:55 ubuntu syncthing: [IH25Q] INFO: GUI and API listening on 127.0.0.1:8384
Feb 18 15:17:55 ubuntu syncthing: [IH25Q] INFO: Access the GUI via the following URL: http://127.0.0.1:8384/