It is very difficult to see the work that has gone into making this module work in modern Drupal. The 8.x-2.x branch is not listed on the module page, but is in all releases, but cannot install due to not supporting Drupal 10 or PHP 8 (the later of which stymies even the Composer Drupal Lenient plugin).
I only happened to notice the 3.0.x branch and 4.x branch when i went to clone the 2.x branch to try to make it compatible with the latest Drupal and PHP.
Reference one or both of these branches on the project page, first by creating development releases for both (so they show up in the Version tag here also!) and then linking to those releases, with as many caveats about development state as you wish but at the very least people like me should be able to see where to test and contribute more easily!
https://git.drupalcode.org/project/entity_merge/-/tree/3.0.x?ref_type=heads
https://git.drupalcode.org/project/entity_merge/-/tree/4.x?ref_type=heads
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