The 1981 planet of the apes movies were re-edited versions of the episodes with new footage. The new footage can still be found, and so can the episodes but the movies are themself lost. The footage can be found at https://youtu.be/klS9zFS4ZbI

Back to the Planet of the Ape:

Galen footage 1
Episode 1: Escape from Tomorrow
Episode 2: The Trap
Galen footage 2

The Forgotten City of the Planet of the Apes:

Galen footage 3
Episode 1: The Gladiators
Episode 2: The Legacy
Galen footage 4

Treachery and Greed on the Planet of the Apes:

Galen footage 5
Episode 1: The Horse Race
Episode 2: The Tyrant
Galen footage 6

Life, Liberty and Pursuit on the Planet of the Apes:

Galen footage 7
Episode 1: The Surgeon
Episode 2: The Interrogation
Galen footage 8

Farewell to the Planet of the Apes:

Galen footage 9
Episode 1: Tomorrow’s Tide
Episode 2: Up Above the World So High
Galen footage 10

https://planetoftheapes.fandom.com/wiki/Planet_of_the_Apes_TV_movies

Mod Edit: see lorang’s posts below in this thread for information on a project release.