Forge for Minecraft version 1.17 requires the use of Java 16 to run and has a different setup than older versions of forge.
For older versions of forge, please see this guide
Download the Installer for the version of forge you wish to run from the forge website
Run the installer on your PC.
Select the "Install server" option
Click the [...] button to specify where to install the files to.
Press the OK button to run the installer.
After it has finished installing the files, go to where they were installed to.
Navigate to /libraries/net/minecraftforge/forge/<ForgeVersion>/
Find and copy the unix_args.txt and paste it into the libraries folder
Upload the libraries folder to the root directory of your minecraft server. It is recommended you use an FTP client
Using an FTP Client
Select the forgejava16 option in the "Jar File" dropdown list in multicraft.
Click the save button to save your changes.