DaemonUmbra

We currently provide user support for 1.14.4 and 1.15.2 versions of Forge, other versions should work (personally when I've seen people ask for help with them the answer is usually user error staring them in the face) but we won't provide assistance if they break. Mods should only ever be installed by putting the jar file in the mods folder (inside .minecraft, look it up on the Minecraft wiki), if a mod tells you it needs anything more than that (barring putting other mods in the mods folder), be very suspicious.

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Without the square brackets...

Yes

The issue detailed in that thread isn't a thing anymore, just run it from the command line without the IPv4 bit

What Minecraft version are you using?

Show your mod in the mods folder with the address bar visible and provide debug.log as described in the Logs section of my signature below

Custom forge mod meaning what exactly?

Vehicles is not a client side mod... where did you get that idea?

Welcome to the world of Modded Minecraft. Mods cannot be used across Minecraft versions, and from the looks of this log the mods you installed are for 1.12.2 or earlier, which we no longer provide user support for. I recommend finding mods that are made for one of the supported versions (1.14.4 and 1.15.2, more info in the thread currently linked in the announcement at the top of every page). I understand that this may not be the answer you wanted to hear, but we try to stay with the most up to date versions of the game.

Provide the installer log of a run where you actually clicked "install client"

Please don't Necro old threads, if you have an issue make your own.

Run the 1.15 installer manually and tell me what it says

That log is basically useless, it looks like you just started the installer when I asked for the log and didn't actually tell it to run the install process. That image shows the installer warning you that it couldn't get a bunch of stuff, you thought you could just carry on? You did not install the version of Java that I told you to install.

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Use imgur for screenshots

That's the crash log, not the debug.log

I blame this one on CurseForge, a 1.15.2 version exists for Forge but you need to go to the full file list to find it

If you installed Java properly you should be able to run the installer by double clicking on it

Look up how to run a jar file from a terminal window and provide the error that it spits out

Did you set your firewall to allow Java through it?

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

You're giving your external IP to your friends and not your internal IP, right?

Please show the error that it spits out when you try to run the installer. Note that the launcher is useless without everything else in place

Install Java