I was able to reproduce the issue on a Windows sandbox and found a working solution. For anyone facing the issue, please try the following steps and let us know whether that works for you:
- Open https://app.ankihub.net/ in Microsoft Edge.
- Click the lock icon in the address bar then click on “Connection is secure”
- Click on the icon to the right
- Go to the Details tab and click the Export button
- Save the file somewhere (e.g. Downloads or Desktop)
- Open the file then click the Install Certificate button.
- Accept the default options by clicking Next
- After clicking Finish the following message should appear and you should now be able to log in to AnkiHub in the add-on.