The latest version of fabric API released December 30th causes a crash with optifbric,
[1.16.4] Fabric API 0.29.0 + optifabric Crashes before the loading screen
[1.16.4] Fabric API 0.28.4 + optifabric-1.8.13 Boots and runs fine

Temp fix
Downgrade fabric API to [1.16.4] Fabric API 0.28.4 to keep playing until an official fix is release

I am aware that this is probably a duplicate of issue 128 But im posting anyways because I've identified the cause with my crash. added a temp fix and a log
latest.log

Ongoing logs for fabric api updates
Crash Log Fabric API-0.29.0+1.16.jar
Crash Log Fabric api-0.29.1+1.16.jar
Crash Log Fabric api-0.29.2+1.16.jar
Crash Log fabric-api-0.29.3+1.16.jar

Update
FabricAPI has updated their jar again on 2021/1/1 and the crash is still present.
here is an updated Crash Log for fabric-api-0.29.1+1.16.jar

Update
FabricAPI has been updated to 0.29.2
Here is the Crash Log for fabric-api-0.29.2+1.16.jar

Update not sure if these are helpful or not
FabricAPI has been updated to 0.29.3
Here is the Crash Log for fabric-api-0.29.3+1.16