Downloaded the June 2019 copy of NC 4.2 - no modifications.  I built the solution in VS2019 as instructed, then launched, and the following error message occurred:
A plugin with 'DiscountRequirement.MustBeAssignedToCustomerRole' system name is already defined

It's been a while since I installed 4.2 fresh (last time it was on VS2017 and I don't recall this bug/error/feature happening before.  Should I try a later copy of NC 4.2 ?
Anyone know how to fix?

Addendum: Rebuilding the brand new, unmodified solution failed now with a bunch of messages (for every plugin)
Severity  Code  Description  Project  File  Line  Suppression State
Error  MSB3030  Could not copy the file "D:\Sites\NopCommerce4.2\Presentation\Nop.Web\Plugins\Payments.Qualpay\Areas\Admin\sitemap.config" because it was not found.  Nop.Plugin.Payments.Square  C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets  4570  


I'll keep trying different things. (18 hours of fighting variations on another project and 4 hours wasted trying to get a virgin copy of Nop to work -me thinks VS2019 is pure junk) MADNESS