Module '"@angular/core"' has no exported member 'OpaqueToken'

TypeScript code generated from swagger.json as part of MSBuild process using this in the csproj:

  <Target Name="NSwag" BeforeTargets="Compile" Outputs="$(ProjectDir)/src/app/code/api.ts"  Condition="Exists('$(ProjectDir)swagger.json')">
    <Message Importance="High" Text="Generating Api.ts from swagger.json." />
    <Exec Command="$(NSwagExe_net60) openapi2tsclient /input:swagger.json /output:$(ProjectDir)/client/src/app/code/api.ts /ClassName:Api /Template:Angular /RxJsVersion:7.8" />
  </Target>

However the resulting output doesn't even build let alone run.

Error: src/app/code/api.ts:13:40 - error TS2305: Module '"@angular/core"' has no exported member 'OpaqueToken'.

Also

Error: src/app/code/api.ts:146226:5 - error TS4114: This member must have an 'override' modifier because it overrides a member in the base class 'Error'.

146226     message: string;
           ~~~~~~~

Start with the generated client/src/app/code/api.ts and the NSwag target in the csproj, then trace the Angular template used by the /Template:Angular option. Check how the generated code references OpaqueToken and declares the Error-derived message member. Done means the generated TypeScript builds without these Angular and override errors.