enable custom title/menus on linux (#62866)

src/vs/code/electron-main/window.ts

@@ -170,11 +170,7 @@ export class CodeWindow implements ICodeWindow {
 				useCustomTitleStyle = false; // not enabled when developing due to https://github.com/electron/electron/issues/3647
 			}
 		} else {
-			if (isLinux) {
-				useCustomTitleStyle = windowConfig && windowConfig.titleBarStyle === 'custom';
-			} else {
-				useCustomTitleStyle = !windowConfig || !windowConfig.titleBarStyle || windowConfig.titleBarStyle === 'custom'; // Default to custom on Windows
-			}
+			useCustomTitleStyle = !windowConfig || !windowConfig.titleBarStyle || windowConfig.titleBarStyle === 'custom'; // Default to custom
 		}
 
 		if (useNativeTabs) {

src/vs/workbench/electron-browser/main.contribution.ts

@@ -813,7 +813,7 @@ configurationRegistry.registerConfiguration({
 		'window.titleBarStyle': {
 			'type': 'string',
 			'enum': ['native', 'custom'],
-			'default': isLinux ? 'native' : 'custom',
+			'default': 'custom',
 			'scope': ConfigurationScope.APPLICATION,
 			'description': nls.localize('titleBarStyle', "Adjust the appearance of the window title bar. Changes require a full restart to apply.")
 		},