A system based on a Z370 motherboard, a compatible CPU (i3/i5/i7) and a supported graphics card (CPU integrated graphics or AMD RX cards for example) should be compatible with MacOS High Sierra and Mojave.
You should try to find someone with a newer Mac (2012 or later) or a working hackintosh running El Capitan 10.11.6 or later to download High Sierra or Mojave.