I was able set negative values. Are you using cinemachine and which version of unity you have?
Viewing post in Exploration of unexplored island (Kenney Jam 2023) comments
The game uses cinemachine and the Unity version is 2019.4.40f1 (Honestly I should switch to a newer LTS version).
Edit: I just did some research and an Unity dev mentions that ortho can be set to negative values for newer version of Unity. So, I'm going to fix this issue by changing to a newer version.
Thank you again for your input. Now we have a way to fix this issue! :D