How to migrate from MySQL 5.7 to 8.0 non-inplace

Hi I have a new Ubuntu 20.04 server, and an old 18.04 server which I am retiring. 18.04 runs MySQL 5.7 and 20.04 runs MySQL 8.0. In the old days, I’d simply do a mysqldump –all-databases and then import it all, including the mysql.* db & schema. Easy. Obviously this is no longer possible with the differences between 5.7 and 8.0.

I have scoured the web and so far I cannot find anything that says how I can upgrade from 5.7 to 8.0. I can’t ask all my database customers for their passwords, so how do I migrate the mysql.users data?