ConcurrentModificationException
Reading crash logs takes knowing the vernacular as well as knowing at least a little bit of what's going on under the hood in that specific case, though a general understanding of programming principles is always a good start.
Making updates to software is not the same as porting a framework from one programming language to another.
There is also the fact that Bedrock Edition (the multiplatform/console version) is written in C++, which cannot be decompiled and examined in the way Java can.
Even if Bedrock could be decompiled there is no promise that the internals are even remotely similar.
Thread Closed.
As Lex has said:
The simplest way would be to open Powershell with the right-click method, then type in cmd and press enter, this will swap to a command prompt while using the same window and staying pointed at the same folder, then use the command given in the other thread.
From the looks the server is crashing when it tries to read one of them, if there's nothing in them just delete them, and remember to use /stop to stop the server cleanly.
It depends on what you mean by "installed".
Optifine can run with or without Forge, but the installation procedures are different.
Double clicking and having Optifine install itself will have it add itself as a game version, this method would not allow Forge to run.
Dropping Optifine into your mods folder will have Forge run Optifine as a mod.
Note that Forge run Optifine does not always work as Optifine's nature means it's devs have to pick specific Forge versions and do their best not to tread on Forge's toes.
These specific Forge versions are noted in Optifine's changelog for each version.