DaemonUmbra

I would recommend directly uploading the file instead of copypasting

Use a paste site to upload the whole thing. (list in my signature)

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

Please provide C:\Users\ethan\AppData\Roaming\.minecraft\config\fml.toml, then delete it and try again. (This is an issue we're trying to diagnose and we need samples of the corrupted configs)

Is it a mod you made or are you trying to update someone else's mod?

We don't keep track of places that provide support for old versions.

Why limit yourself to 1.16.3? Especially since 1.16.5 just came out and fixes crash bugs that could be abused to render a server unusuable.

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

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

What ISP do you have? Sounds like they suck

Are you using mods or making them?

The bit before the (MavenPublication) is simply the name of the publication. The bit inside the brackets is what gets published, GitHub is suggesting publishing everything built from Java, which may or may not be what you want, I recommend testing by publishing to mavenLocal or mcmodsrepo first. All in all GitHub Packages should just be a maven that requires authentication

No idea, I don't own a Mac. Try google.

That sounds like a connection issue, what exactly is the setup you have and is there a specific reason to not host a dedicated server locally?

Lex has said that he'll poke around with it when he gets his Mac Mini... however until he gets it and starts poking around there is literally nothing any of us can do because none of us own Macs and we're not all that motivated to go out and buy something expensive, therefor giving money to the same company that broke what you're asking us to fix.

Delete C:\Users\admin\AppData\Roaming\.minecraft\config\fml.toml and try again.

Does it mention anything about checking a console for the error?

Really old Minecraft versions are no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Uninstall every version of Java that you have and then reinstall whatever Java versions you need. Note: I don't mean reinstall them one by one I mean there needs to be a point where there is one version of Java left and it gets uninstalled so it will clear out shared stuff to be regenerated when you reinstall the new one.

Try Johann Löfflmann's JarFix utility.

This sounds like you're starting a vanilla server, how are you starting the server?

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

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

Use datagens