Using IDesignTimeDbContextFactory to generate migrations at design time, running Package Manager Console commands add-migration, update-datebase, etc.
Microsoft.EntityFrameworkCore.Design now being a DevelopmentDependency type package, adds this to the .csproj where EFCore resides so that it cannot be referenced up the chain:
<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
Nice idea, but this breaks running design time migration commands from PMC (which gives an error about the startup project needing Microsoft.EntityFrameworkCore.Design)
Design time migration tooling needs a reference to Microsoft.EntityFrameworkCore.Design but the default DevelopmentDependency entries in the .csproj file appear to be blocking.
Temp solution - comment out the <PrivateAssets/> element in the .csproj file, then PMC migration commands work
<!-- <PrivateAssets>all</PrivateAssets> -->