Categories widget / Error message in the widget area

After the update, we noticed that the blog categories were no longer displayed in the sidebar. When we go into the Widgets section in WordPress, we can see the individual widgets but cannot manage them. When we call up the live preview, the following error appears:

Fatal error: Uncaught Error: Call to undefined function mysql_error() in /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/db.class.php:29 Stack trace: #0 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/db.class.php(124): UniteDBRev->checkForErrors(‘fetch’) #1 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/revslider_slider.class.php(720): UniteDBRev->fetch(‘wp_revslider_sl…’, ”, ‘id’) #2 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/revslider_slider.class.php(756): RevSlider->getArrSliders() #3 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/revslider_widget.class.php(19): RevSlider->getArrSlidersShort() #4 /home/artwin.ch/wwwbeta/wp-includes/class-wp-widget.php(519): RevSlider_Widget->form(Array) #5 /home/artwin.ch/wwwbeta/wp-admin/includes/widgets.php(274): WP_Widget->form_callback(Array) #6 /home/artwin.ch/wwwbeta/wp-includes/class-wp-customize-widgets.php(1050): wp_widget_control(Array, Array) #7 /home/artwin.ch/wwwbeta/wp-includes/class-wp-customize in /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/db.class.php on line 29

We also received the following additional information by e-mail:

WordPress-Version 5.6.1
Current theme: Minicorp (version 2.5)
Current plugin: Revolution Slider (version 2.3.6) PHP version 7.3.27

An error of the type E_ERROR was found in line 29 of the file /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/db.class.php verursacht. Fehlermeldung: Uncaught Error: Call to undefined function mysql_error() in /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/db.class.php:29
Stack trace:
#0 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/db.class.php(124): UniteDBRev->checkForErrors(‘fetch’)
#1 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/revslider_slider.class.php(720): UniteDBRev->fetch(‘wp_revslider_sl…’, ”, ‘id’)
#2 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/revslider_slider.class.php(756): RevSlider->getArrSliders()
#3 /home/artwin.ch/wwwbeta/wp-content/plugins/revslider/inc_php/revslider_widget.class.php(19): RevSlider->getArrSlidersShort()
#4 /home/artwin.ch/wwwbeta/wp-includes/class-wp-widget.php(519): RevSlider_Widget->form(Array)
#5 /home/artwin.ch/wwwbeta/wp-admin/includes/widgets.php(274): WP_Widget->form_callback(Array)
#6 /home/artwin.ch/wwwbeta/wp-admin/includes/widgets.php(60): wp_widget_control(Array, Array)
#7 /home/artwin.ch/wwwbeta/wp-admin/widgets.php(452): wp_list_widgets()

Do you know this problem?