When France talks about 'Separatisme' it's worth noting this is not their own invention or bogeyman, it is a recognition of an explicit strategy pursued by Islamist groups. Qaradawi, the most influential Islamist in the world today, openly advocates against "assimilation" https://twitter.com/LiamSD12/status/1334222908978245639

Qaradawi: followers should create "their own religious, educational and recreational establishments." He explicitly uses the terms "Muslim ghetto": "have your small society within the larger society"

Qaradawi: "It is the duty of the Islamic Movement" - (how the Muslim Brotherhood often refer to themselves) - "not to leave these expatriates (Western Muslims) to be swept by the whirlpool of the materialistic trend that prevails in the West."

On the other hand, Qaradawi and other leading Islamists do advocate engagement in society and do not advocate total isolation. A cynic might suggest this is purely transactional, and only useful insofar as Islamists can influence wider society & benefit from it.

In France, the cross-pollination between Islamist & Activist Salafi thought has arguably led to a more 'separatist' element in some places. As Salafists advocate total loyalty to everything Islamic (or rather their interpretation), & total disavowal & even hostility to all else.

Qaradawi and other leading Islamists do not necessarily believe in actively pursuing their ultimate objectives, rather that their gradual influence (even if it takes decades) on these communities & identity would eventually wither away opposition to their overall political vision