[Samsung Galaxy S10+ Questions & Answers] Quentoche:
Thanks for your answer. I did not think about the logs.

Here's what's happening when typing *#2663# :

11-24 21:34:19.419 3328 3328 E AndroidRuntime: FATAL EXCEPTION: main
11-24 21:34:19.419 3328 3328 E AndroidRuntime: Process: android.uid.system, PID: 3328
11-24 21:34:19.419 3328 3328 E AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sec.android.app.factorykeystring/com.sec.android.app.status.touch_firmware}: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3113)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3256)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1947)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.os.Handler.dispatchMessage(Handler.java:106)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.os.Looper.loop(Looper.java:214)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.ActivityThread.main(ActivityThread.java:7037)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at java.lang.reflect.Method.invoke(Native Method)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
11-24 21:34:19.419 3328 3328 E AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.sec.android.app.status.touch_firmware.writeCmd(touch_firmware.java:1506)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.sec.android.app.status.touch_firmware.readCmdResult(touch_firmware.java:1661)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.sec.android.app.status.touch_firmware.readThreshold_melfas(touch_firmware.java:1864)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.sec.android.app.status.touch_firmware.updateText(touch_firmware.java:912)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.sec.android.app.status.touch_firmware.init(touch_firmware.java:902)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at com.sec.android.app.status.touch_firmware.onCreate(touch_firmware.java:339)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.Activity.performCreate(Activity.java:7327)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.Activity.performCreate(Activity.java:7318)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3093)
11-24 21:34:19.419 3328 3328 E AndroidRuntime:	... 11 more