The Walking Dead evidently completed filming for all 16 episodes of Season 10, but post-production wasn’t completed when the show came to a halt due to the coronavirus pandemic.
Another TV show ran out of episodes prematurely for the same reason, but at least AMC could reveal the plan for the finale.
Episodes of The Walking Dead undoubtedly require significant effects in post.
The decaying looks and snarling of the zombies must take a lot of time and effort, not to mention the stunts!