Tapping in the Search box does not bring up the touch keyboard"

What is your current Mixxx version?

Is the issue with the latest alpha?
See http://mixxx.org/forums/viewtopic.php?f=1&t=6617

I've been using version 1.11.0 build r3862. I haven't tried it with the current alpha but certainly can.

[Expired for Mixxx because there has been no activity for 60 days.]

I can confirm the issue with Ubuntu Bionic and Onboard on screen keyboard.

Normally Qt should show a keyboard for all widgets that have the "Qt::WA_InputMethodEnabled" enabled.

You can also set the QStyle::RSIP_OnMouseClick to decide that the keyboard appearance is delayed until the Widget was clicked.

Qt calls:
QGuiApplication::inputMethod()->show();
Which uses the abstract class QPlatformInputContext::showInputPanel() to call the target specific function. In case of Linux it is QIBusPlatformInputContext, without a override function for showInputPanel()

Than there is also QApplication::setAutoSipEnabled() to control keyboard behavior.

In case of IBUS there must be something magic to control if the Keyboard should be shown or not.

When entering the preferences,the keyboard is shown and hidden over and over again.
This bouncing can also be seen in the Qt based VLC player.

So I guess there must be a general issue.

The search box does not show the keyboard at all.

This can be fixed by adjusting the style.
https://github.com/mixxxdj/mixxx/pull/3231

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7939