You can also switch to a software renderer by downloading and copying a few files into your Slicer folder as described here: Get Help — 3D Slicer documentation
Software renderers are slower, but the performance degradation is only significant if you use volume rendering or display a complex model.
I also downloaded the latest version, 4.8.1 . I could run the app successfully. However, the extensions can’t be downloaded. It seems the extension link is outdated: http://slicer.kitware.com/midas3/slicerappstore
I’m not sure what hardware you are using, but there’s a good chance that installing linux (e.g. ubuntu) on your hardware will enable a newer version of Slicer. If you are able to consider new hardware, Chromebooks can be a very cost-effective option and many run Slicer well.