System.Windows.Forms.dll assembly is referenced by user code, but is not supported on StandaloneLinuxUniversal platform

Maybe you're missing the -buildTarget parameter. Did you try building with the application first? It could be related to using command line to build. I personally had success building from the command line using something that looks like this:

 export UNITY_PATH=/Applications/Unity/Unity.app/Contents/MacOS/unity
 
 export BUILD_TARGET=StandaloneLinuxUniversal
 export BUILD_TARGET_GROUP=Standalone
 
   ${UNITY_PATH} \
   -projectPath $(pwd) \
   -quit \
   -batchmode \
   -buildTarget ${BUILD_TARGET} \
   -customBuildTarget ${BUILD_TARGET} \
   -customBuildTargetGroup ${BUILD_TARGET_GROUP} \
   -customBuildOptions AcceptExternalModificationsToPlayer \
   -executeMethod BuildCommand.PerformBuild \
   -logFile

I had to write my own build script Assets/Editor/BuildCommand.cs with method PerformBuild which sets BuildTarget and BuildTargetGroup taken from arguments. I mostly started from examples given in https://docs.unity3d.com/Manual/CommandLineArguments.html

It looks something like this:

 using UnityEngine;
 using UnityEditor;
 using System.Linq;
 using System;
 
 static class BuildCommand
 {
     static string GetArgument (string name)
     {
         string[] args = Environment.GetCommandLineArgs ();
         for (int i = 0; i < args.Length; i++) {
             if (args [i].Contains (name)) {
                 return args [i + 1];
             }
         }
         return null;
     }
 
     static string[] EnabledScenes ()
     {
         return (
             from scene in EditorBuildSettings.scenes
             where scene.enabled
             select scene.path
         ).ToArray ();
     }
 
     static BuildTarget GetBuildTarget ()
     {
         string target = GetArgument ("customBuildTarget");
         Console.WriteLine (":: Received customBuildTarget " + target);
 
         return (BuildTarget)Enum.Parse (typeof(BuildTarget), target);
     }
 
     static BuildTargetGroup GetBuildTargetGroup ()
     {
         string targetGroup = GetArgument ("customBuildTargetGroup");
         Console.WriteLine (":: Received customBuildTargetGroup " + targetGroup);
         return (BuildTargetGroup)Enum.Parse (typeof(BuildTargetGroup), targetGroup);
     }
 
     static string GetBuildPath ()
     {
         string buildPath = GetArgument ("customBuildPath");
         Console.WriteLine (":: Received customBuildPath " + buildPath);
         if (buildPath == "") {
             throw new Exception ("customBuildPath argument is missing");
         }
         return buildPath;
     }
 
     static BuildOptions GetBuildOptions ()
     {
         string buildOptions = GetArgument ("customBuildOptions");
         return buildOptions == "AcceptExternalModificationsToPlayer" ? BuildOptions.AcceptExternalModificationsToPlayer : BuildOptions.None;
     }
 
     static string getEnv(string key, bool secret = false, bool verbose = true) {
         var env_var = Environment.GetEnvironmentVariable(key);
         if (verbose) {
             if (env_var != null) {
                 if (secret) {
                     Console.WriteLine(":: env['" + key + "'] set");
                 } else {
                     Console.WriteLine(":: env['" + key + "'] set to '" + env_var + "'");
                 }
             } else {
                 Console.WriteLine(":: env['" + key + "'] is null");
             }
         }
         return env_var;
     }
 
     static void PerformBuild ()
     {
         Console.WriteLine (":: Preparing build");
         BuildPlayerOptions buildPlayerOptions = new BuildPlayerOptions ();
         buildPlayerOptions.locationPathName = GetBuildPath ();
         buildPlayerOptions.options = GetBuildOptions ();
         buildPlayerOptions.scenes = EnabledScenes ();
         buildPlayerOptions.target = GetBuildTarget ();
         buildPlayerOptions.targetGroup = GetBuildTargetGroup ();
 
         Console.WriteLine ("locationPathName: " + buildPlayerOptions.locationPathName);
         Console.WriteLine ("target: " + buildPlayerOptions.target);
         Console.WriteLine ("targetGroup: " + buildPlayerOptions.targetGroup);
         Console.WriteLine ("scenes: " + buildPlayerOptions.scenes);
         Console.WriteLine ("assetBundleManifestPath: " + buildPlayerOptions.assetBundleManifestPath);
 
         Console.WriteLine (":: Performing build");
         BuildPipeline.BuildPlayer (buildPlayerOptions);
         Console.WriteLine (":: Done with build");
     }
 }