Just a quick question. Does MediaWiki 1.35.2 and later still support Composer 1? It looks like it. Perhaps someone has already run into this requirement and can share experience ...
Topic on Project:Support desk
Self answering my question: Affirmative. It is possible to handle your 1.35.x with Composer 1 after updating to 2.x of the merge plugin. This is great since I can wait with the upgrade from Composer 1 to Composer 2 until I have upgraded all wikis on the respective server from 1.31.x to 1.35.x.