Can't find Mojave on App Store

I'm trying to download a mojave installer to create a bootable usb so that I can do a clean install on a new hard drive. I can't seem to find the mojave installer on the App Store though. When I click the direct link in Step 4 (https://support.apple.com/en-sg/HT210190), it prompts me to open the link in iTunes or App Store. I select App Store. App Store launches, and there is a "Loading" message. After a while, it says "Cannot connect to app store". The odd thing is my App Store does work - I can find and download other apps using the App Store. Even the direct link to download Catalina works. Please help. Thanks.