Bloater, which is the name of the large mushroom zombie that you mentioned, was also a real actor in prosthetics.

Source: https://www.macleans.ca/culture/television/the-last-of-us-location-manager-on-how-hbo-transformed-alberta-into-a-zombie-wasteland/

Now we need to address the hulking monster in the room – the Bloater that crawls menacingly from underground with the rest of the infected, boasting incredible strength, the ability to use echolocation and a near-impenetrable exterior.

Source: https://metro.co.uk/2023/02/11/the-last-of-us-episode-5-behind-the-scenes-of-battle-with-bloater-18258456/

Stunt performer Adam Basil, who played the Bloater, told Entertainment Weekly that he believes the monster has become a "bit of a sex icon."

Source: https://comicbook.com/gaming/news/the-last-of-us-hbo-bloater-sex-icon/

We get a few close-up moments with the Bloater as he emerges from the ground, striking fear into the hearts of the audience, and then when he ) head from his body.

Source: https://collider.com/the-last-of-us-show-bloater-vfx/