The Popular Front didn't 'name' him (unless you mean the article). In fact, parties won't 'get' to name anyone, that's the prsident who will pick the PM. However, he has to pick a PM whom a majority of the National Assembly (being elected here) will support, lest it gets 'censored' (destitued) by the Parliement.

JLM is the leader of LFI (even if, particularly in the creation of the Popular Front, his detractors are slowly getting the better of him), and he was LFI's candidate for the 2022 Presidential Election. What the article mentions is that a few days ago, he mentioned on TV that he feels 'capable' of endorsing the role of PM. That does NOT mean the rest of the alliance will suport him (in fact, there's a 0% chance the socialists will).

The people who are more likely to be named as PM (if the Popular Front wins a majority of the Assembly), are either François Ruffin (also LFI, but highly popular, is the one who launched the movement for this Popular Front, and a detractor of Melanchon's), or somebody more moderate without much political clout used to serve as the one on the ejectable seat when Macron's term is over (and said PM is likely to have become unpopular by then).

For their program, I unfortunately wasn't able to find a translation nor a summary in english (tbf, it was published just this friday).

Le Monde has a summary (in french) which you can translate with your favorite translator app if you want.