I've installed Linux on an old computer. I got the printer working but still can't get network sharing to work. On my windows 10 computer, I was searching for information when I clicked on a link to go to http://ubuntuportal.com I got an error message saying, Your connection is not private.
Usually, there is a link to go to this page, but it wasn't noticeable at first. So I clicked on the Help me understand option at the bottom of the message. This then gave me the link I was looking for. I clicked on Proceed to ubuntuportal.com (unsafe). Unsafe here means unsecured connection.
According to the message, their security certificate only expired the day before. This error message also mentioned checking the date on your computer. If you keep getting error messages like this, it could be the date on your computer. Web-browsers have certificates that have a start date and an end date. If the date on your computer is too far off, one way or the other, you'll get similar error messages on all browsers.