Download and install from Atlassian Marketplace: https://marketplace.atlassian.com/apps/1212145/threaded-comments-for-jira?hosting=server&tab=installation
Only applicable for Jira Server or Jira Data Center.
Supported versions from 8.0.0 to 8.18.2
Version 1.33.0 for Jira Server and Jira Data Center 8.0.0 - 8.18.2
Released:- Aug 9th, 2021
Configuration guide can be found here.