It appears that the potential rematch between Ngannou and UFC heavyweight champion Stipe Miocic may not happen until next year and Ngannou vented his frustrations with a series of posts on Twitter (via MMA Fighting):
2 title fights in the @ufc heavyweight division for the past two years and yet we don't know if there will be another one anytime soon. Contenders have to fight for something #ThisIsSucks
Apparently Stipe is out until March. If I have to wait until then it'll be almost another year between fights.
I fought once for 20 seconds in the last 16 months
Ngannou and Miocic met for the first time at UFC 220 in January of 2018, where Miocic scored a unanimous decision win over Ngannou to retain the UFC heavyweight title.