I don't know if this has been mentioned here before, but the BBC are reporting that Logan Sargeant is to fill the second seat alongside Alex Albon at Williams providing that Sargeant makes enough points to qualify for a Superlicence. The BBC say that he should get enough from his position in F2 where he is currently in 3rd place overall, or, if not, by taking part in two more F1 free practices.
https://www.bbc.co.uk/sport/formula1/63361131