DaemonUmbra

Looks like something went wrong with the installation, delete the libraries folder and both jars and rerun the installer

Please provide debug.log from the server's logs folder (please use one of the paste sites listed in my signature below)

Does it say anything in the cmd window that pops up?

Congrats... you're running a Vanilla server. Rename server.jar back to minecraft_server.1.16.5.jar like it's supposed to be and change your bat file to run the Forge jar.

I'm trying to confirm which jar you renamed... better yet just provide a screenshot of your server folder

So is that a yes or a no?

So you renamed the jar that was originally called minecraft_server.1.16.5.jar and are running that from your bat file?

Which jar did you rename and why did you rename it?

It does... what's in that bat file?

What file are you using to start the server?

First of all remove Optifine from your server, it's a client only mod and just another thing to go wrong on the server side. How important is this world save?

Forge installs itself as if it was a version of Minecraft, if the installer doesn't make a profile you can make one yourself by selecting Forge from the list of Minecraft versions.

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

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

Please read the error...

I told you to delete a file in the save, not the save itself Go into the save and delete forge-server.toml from serverconfig

Well first of all you have Optifine on a server, which is pointless and only adds a possible point of failure. Second, why are you using 1.16.1?

Ok so in modern versions of Forge, server configs are save-specific, and your server config has become corrupted, delete it

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

Guess which file you need to delete now

Send it via google drive I guess

Show your mods.toml

Delete config/titanium/modules.toml and try again

Don't try to share the folder, zip it up first

Can you provide the world save please?