If they're francophone immigrants, I would imagine their French is already pretty good. I'd like to add to my response earlier. If we want to make sure that francophone immigrants can maintain or improve their French, we need to enable them to live and receive services in French. We need to ensure institutional completeness.
During the pandemic, lots of people who had learned French lost it because of the circumstances. It all ties into the earlier discussion about the territorial aspect and communities. If the conditions are right for people to live their lives in French, they'll participate and maintain their language. Sometimes a job in English is inevitable, but these people can live their lives in both languages. Francophones in minority communities live in both languages. Nobody tells them not to speak English or not to work in an English-speaking workplace.
People talked about bilingualism. The idea is to make sure people have the opportunity to live in both languages.