this may be the same as a issue below but i saw they did not included any version info so i made this.
this is a random startup issues does not happen every time but when it does it crashes and gives the report below i just noticed there is a new version ill test that one as well and let you know its it also has startup crash.

Minecraft 1.16.4
Forge 35.1.13
create-mc1.16.3_v0.3a
Crash report https://pastebin.com/Auh064KV

This was addressed in 0.3e, feel free to re-open if its still an issue. Cheers~