We have plenty of successful cases with OpenCore on both Z390 and Z490. In fact, 100% of Z490 installations are done with OpenCore.
If you have a spare SSD, then yes I would certainly recommend a fresh installation. If you create the OpenCore 0.6.0 EFI folder on a USB flash disk
and unlock MSR 0xE2, then you can install Mojave or Catalina by following the Z490 Vision D guide (yes, you read that right) but
skipping Steps 4, 5, 6, 7. The Z490 guide is located here:
CaseySJ's Comet Lake-S in BeQuiet! Pure Base 500DX: Gigabyte Z490 Vision-D - i5-10400 - UHD 630 - AMD RX 580 (Please do not quote this guide in its entirety. Post a link instead.) (See this post for how to refer to a Guide or Mini-Guide.) Refer to the Z390 Designare thread for answers to a...
www.tonymacx86.com
If you decide to do this, feel free to compress and upload your OpenCore EFI folder. You may in fact send it via Private Message (so you don't have to remove serial numbers). I can double-check it before you begin.