BSP is part of the JVM plugin

main/src/main/scala/sbt/Defaults.scala

@@ -240,7 +240,7 @@ object Defaults extends BuildCommon {
       bgCopyClasspath :== true,
       closeClassLoaders :== SysProp.closeClassLoaders,
       allowZombieClassLoaders :== true,
-    )
+    ) ++ BuildServerProtocol.globalSettings
 
   private[sbt] lazy val globalIvyCore: Seq[Setting[_]] =
     Seq(
@@ -386,8 +386,7 @@ object Defaults extends BuildCommon {
         sys.env.contains("CI") || SysProp.ci,
       // watch related settings
       pollInterval :== Watch.defaultPollInterval,
-    ) ++ BuildServerProtocol.globalSettings
-      ++ LintUnused.lintSettings
+    ) ++ LintUnused.lintSettings
       ++ DefaultBackgroundJobService.backgroundJobServiceSettings
   )
 

main/src/main/scala/sbt/internal/server/BuildServerProtocol.scala

@@ -39,7 +39,9 @@ object BuildServerProtocol {
           bspTargetConfigs.toSeq.map(name => Scope.Global.in(ref, ConfigKey(name)))
       }
       Def.setting {
-        val targetIds = scopes.map(_ / Keys.bspTargetIdentifier).join.value
+        val targetIds = scopes.map(_ / Keys.bspTargetIdentifier)
+          .map(_?) // bspTargetIdentifier might no be defined if the JvmPlugin is disabled
+          .join.value.flatten
         targetIds.zip(scopes).toMap
       }
     }.value,