The Oni Mod Depot is only available without SSL (HTTPS), so you need to access it with http://mods.oni2.net.

If clicking that URL does not work, you'll need to copy-paste it into your browser's address bar.

If that doesn't work either and you're in Firefox, you need to turn off the feature in your browser that forces HTTPS. Currently you should find it at Settings > Security > HTTPS-Only Mode.

If you're in Microsoft Edge, use another browser open Edge's settings and click on "Default browser", set "Allow sites to be reloaded in Internet Explorer Mode" to Allow, then click "Add a page", type in "http://mods.oni2.net" and click Add. Restart the browser and the link above will successfully redirect you to the Oni Mod Depot in HTTP mode.