I strongly dislike Mélenchon's nationalism and narcissism, and his record on Putin is bad. But LFI is not "anti-immigrant": they are the ones who opposed Macron's immigration law
They did so opportunistically, as NUPES. They are not averse to tapping into the same vein of anti-immigrant sentiment that fuels the right. France's Maghrebien population is nowhere represented to the extent that metroLabour represents the UK's South Asian Muslims.