Minecraft Version

1.16.x

Mod Loader

Forge

Mod Loader Version

36.2.35

Mod Version

DefaultOptions_1.16.5-12.2.1.jar

Describe the Issue

Before even saving default options, when you select singleplayer it crashes the client.
Reported on another thread with more details here:
Shadows-of-Fire/PackMenu#41

Logs

Debug.log provided in above post

Do you use any performance-enhancing mods (e.g. OptiFine)?

Rubidium, Oculus, Rubidium/Magnesium extras, Roadrunner

1.16 is no longer supported and the logs paste has expired. Most likely this was a conflict with another mod in the pack as this does not seem to be a widespread issue.