Most of what you said doesn't make sense but:
Make sure you have Java 8 installed.
Make sure the mods and forge are the same version.
Make a start script to run the universal jar.
We can't help you unless you provide us with actual information to help us resolve the issue.
Provide a crash report or let us know if there is a hs_err_pidXXXXX file in the .minecraft folder.
Theres still no crash. If you can provide us with a log that shows the crash please upload that. Otherwise since forge on it own seems to work you can try adding in individual mods to see if there's one or more specific mods causing the game to freeze.
If you're asking if older mods are compatible with 1.16 not they are not.
But installing forge 1.16 it will not break other forge installs as long as you have separate mod folders.
Custom Quests is broken you can try removing its config files or any JSON files for the mod as they may be causing the crash. If that doesn't work remove the mod entirely.
It is mainly just fixing errors but as it is with coding just because there aren't any errors doesn't mean it will work. The things the code does could have changed and some stuff is added or removed entirely.