Dell isn't likely going to test the XPS 8700 for compatibility with Win 10 20H2... My Inspiron laptop from 2013 with i3 CPU is running Win 10 20H2 just fine and Dell hasn't tested it for several  of the latest Win 10 updates. So I suspect your XPS 8700 will run it too. As a safeguard, you might want to create an image of all partitions on the HDD and save it on an external USB drive before running the update, so you can easily revert if necessary. Macrium Reflect (free) is a good tool for creating the image. And also use Macrium to create a bootable USB stick so you can revert easily...  
Has anyone done a successful update to windows 10 20H2 on XPS 8700? I know Dell says it's untested, but don't know if that means I should wait, or give it a go. I have an XPS 8700 Intel i7-4790 CPU 3.6 GHz 8.00 GB memory, 64-bit Windows 10 with all updates (except 20H2) WDC WD10EZEX-75M2NA0 disk drive I would appreciate knowing if anyone's updated successfully, and if so, what steps were taken to do the update.  
XPS 8700, Update to Windows 10 20H2