- Create a branch "maintenance" with the last version before deprecation
- Empty the master branch and only leave a sole README.md file with the added line
"For reference or potential bugfix releases use branch maintenance"
(where "maintenance" is linked to the branch where the code still exists, see https://github.com/apache/sling-org-apache-sling-starter-startup as example)
- Tag the module as
deprecatedusing the .asf.yaml features for git repositories feature. If no such file is present make sure to use the default values from Using Git with Sling#Boilerplatefiles .