Make sure you read the upgrade notes
Upgrade simplified: Languages, Git and SVN, LDAP/GitHub/SAML support now built-in (8.0, 8.5)
All plugins related to languages, Git/SVN support, and LDAP/GitHub/SAML authentication are now built into SonarQube itself. If you were using these plugins, you need to remove them from your extensions/plugins directory before upgrading. Read more in this community guide: SonarQube v8.5 and Beyond: Where did all the plugins go? (MMF-2042)