not trying that upgrade again

ProjectSettings/HDRPProjectSettings.asset

@@ -15,7 +15,7 @@ MonoBehaviour:
   version: 1
   m_ProjectSettingFolderPath: HDRPDefaultResources
   m_WizardPopupAtStart: 0
-  m_WizardPopupAlreadyShownOnce: 0
+  m_WizardPopupAlreadyShownOnce: 1
   m_WizardActiveTab: 0
   m_WizardNeedRestartAfterChangingToDX12: 0
   m_WizardNeedToRunFixAllAgainAfterDomainReload: 0

ProjectSettings/ProjectVersion.txt

@@ -1,2 +1,2 @@
-m_EditorVersion: 2021.2.8f1
-m_EditorVersionWithRevision: 2021.2.8f1 (d0e5f0a7b06a)
+m_EditorVersion: 2020.3.26f1
+m_EditorVersionWithRevision: 2020.3.26f1 (7298b473bc1a)

ProjectSettings/VFXManager.asset

@@ -10,6 +10,5 @@ VFXManager:
   m_RenderPipeSettingsPath: 
   m_FixedTimeStep: 0.016666668
   m_MaxDeltaTime: 0.05
-  m_CompiledVersion: 3
-  m_RuntimeVersion: 20
-  m_RuntimeResources: {fileID: 11400000, guid: bc10b42afe3813544bffd38ae2cd893d, type: 2}
+  m_CompiledVersion: 2
+  m_RuntimeVersion: 12