The UMC404HD works fine with modern versions of Cubase.
Buying a newer computer is recommended. If you don’t have a lot of money to spend, I would recommend buying a Windows computer, which will offer similar performance to a Mac for cheaper.
You can move your files from your old Mac to a new Windows machine by following these instructions:
Please log into your MySteinberg and make sure that your software eLicenser is registered. This will allow you to move your Cubase license to your new computer in the future, and then you’ll be able to upgrade to Cubase Elements 9.5 for just 49 bucks. Compared to your Cubase LE 4, Elements 9.5 will add a crazy amount of new stuff on top of massively improving the workflow and usability. It’s totally worth it.