How to add obfuscator in Azure devops Pipeline for private Nuget feed

Question

I have created a shared .NetStandard2.0 library for my projects. Sample method looks like below:

namespace SharedLibrary
{
    public sealed class MySecrets
    {
        public string GetSecrets()
        {
            // Do some activity
            string mySecreteString = "XXXX";
            return mySecreteString;
        }
    }
}

I have also created Yaml Pipeline that push the Nuget of the library in feeds as below.

trigger:
- main

pool:
  vmImage: 'windows-latest'

variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'
  major: '3'
  minor: '0'
  revision: $[counter(variables['minor'], 1)] # This will get reset every time minor gets bumped.
  nugetVersion: '$(major).$(minor).$(revision)'

steps:
- task: UseDotNet@2
  displayName: 'Use .NetCore SDK'
  inputs:
    packageType: sdk
    version: 3.x
- task: DotNetCoreCLI@2
  displayName: Restore Task
  inputs:
    command: restore
    projects: '**\*csproj'

- task: DotNetCoreCLI@2
  displayName: Build Taks
  inputs:
    command: build
    projects: '**/*csproj'
    arguments: '--configuration Release'

- task: DotNetCoreCLI@2
  inputs:
    command: 'pack'
    packagesToPack: 'SharedLibrary/SharedLibrary.csproj' 
    versioningScheme: 'byEnvVar'
    versionEnvVar:  'nugetVersion'
- task: DotNetCoreCLI@2
  inputs:
    command: 'push'
    packagesToPush: '$(Build.ArtifactStagingDirectory)/**/*.nupkg;!$(Build.ArtifactStagingDirectory)/**/*.symbols.nupkg'
    nuGetFeedType: 'internal'
    publishVstsFeed: 'XXXXX-8335-4cbc-9c43-2db9ad7e4000'

I have learned the .dll can be decompiled. So I have applied followed this Obfuscar reffernce to my project and obfuscar.xml and post build event "$(Obfuscar)" obfuscar.xml to my solution. but the build is failing after adding obfuscar.

enter image description here

Not sure how to make build work after obfuscation in DevOps Also, I happy to implement other way that we can generate obfuscator nuget in Azure Devops pipeline.