To highlight focused tab one can clone konsole repo and add some code there.

src/widgets/TerminalHeaderBar.h, class TerminalHeaderBar definition:

private:
    QPalette m_palette = QPalette();

src/widgets/TerminalHeaderBar.cpp, TerminalHeaderBar::paintEvent() implementation:

void TerminalHeaderBar::paintEvent(QPaintEvent *paintEvent)
{
    if (m_terminalIsFocused) {
        m_palette.setColor(QPalette::WindowText, QColor(200, 200, 50));
        m_palette.setColor(QPalette::Window, QColor(50, 50, 0));
    } else {
        m_palette.setColor(QPalette::WindowText, QColor(200, 200, 200));
        m_palette.setColor(QPalette::Window, QColor(46, 48, 43));
    }

    setPalette(m_palette);