I'm confused about what the term "ltsrel" means. The way I understand it, it *should* mean that the extension supports only Long Term Support versions of MediaWiki. It would have a branch for every LTS version of MediaWiki like REL1_31 and REL1_35, but not for REL1_32, REL1_33 or REL1_34.

However, on the Compatibility page, the rel and ltsrel policies are described as:

* release branches (key: rel): For every MediaWiki release, there is a corresponding branch in the extension. So e.g. if you use MediaWiki 1.36, you should use the REL1_36 branch of the extension.

* long-term support release branches (key: ltsrel): For every MediaWiki release, there is a corresponding branch in the extension, following the Version lifecycle release policy.

These sound exactly alike to me.