Initially the FIFA was planning for a 40 team competition. This was the plan proposed by the then FIFA Gianni Infantino (March 2016). The decision to expand the world cup to 48 teams was taken by the FIFA Council on 2017. But I am not sure about the total number of matches. Initially they were planning for 80, with 3 teams each in 16 groups. But now the format has changed, and there will be 4 teams in each of the 12 groups. So the total number of matches are going to go up to 104. Finalists will play a total of 8 matches.
I have found out 3 teams will play in each group from 16 groups there will be 32 teams in the next knockout round. I don't know why FIFA has to do this in this world cup, but a knockout stage with 32 teams and teams in the group stages only having to play 2 matches before getting out of the tournament or the next round doesn't seem fair enough to me. All the countries, fans and players wait for that event, but their fate is decided in only two matches.