I'm not a modpack developer, but I have basic knowledge to edit values in code, I want to change the damage of the weapons and the hp of entities, but when I tried building the .jar file, I realized that it was for 1.20.

Yes - it was named main. I changed it to 1.19.2 now to avoid confusion 👍
You may be better off changing the item damage using scripting tools such as Kube JS 🤔(not sure how to change the entity HP and stuff though)

Thank you for your help!