We've been using formidable on PHP 7.4.3 for a long time. We now tried to update to PHP 8.0.30, the website itself and the forms on the frontend work, when editing a form in the backend and clicking on the tab "styles", we get an wordpress error: 

Ein Fehler vom Typ E_ERROR wurde in der Zeile 532 der Datei /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/models/FrmStyle.php verursacht. Fehlermeldung: Uncaught Error: Attempt to assign property "post_content" on null in /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/models/FrmStyle.php:532

Stack trace:

#0 /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/controllers/FrmStylesController.php(1095): FrmStyle->get_all()

#1 /home/www/vhosts/redacted.com/httpdocs/wp-includes/class-wp-hook.php(310): FrmStylesController::get_style_opts()

#2 /home/www/vhosts/redacted.com/httpdocs/wp-includes/plugin.php(205): WP_Hook->apply_filters()

#3 /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/controllers/FrmFormsController.php(1363): apply_filters()

#4 /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/views/frm-forms/settings.php(48): FrmFormsController::buttons_settings()

#5 /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/controllers/FrmFormsController.php(1194): require('...')

#6 /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/controllers/FrmFormsController.php(155): FrmFormsController::get_settings_vars()

#7 /home/www/vhosts/redacted.com/httpdocs/wp-content/plugins/formidable/classes/controllers/FrmFormsController.php(1773): FrmFormsController::settings()

#8 /home/www/vhosts/redacted.com/httpdocs/wp-includes/class-wp-hook.php(310): FrmFormsController::route()

#9 /home/www/vhosts/redacted.com/httpdocs/wp-includes/class-wp-hook.php(334): WP_Hook->apply_filters()

#10 /home/www/vhosts/redacted.com/httpdocs/wp-includes/plugin.php(517): WP_Hook->do_action()

#11 /home/www/vhosts/redacted.com/httpdocs/wp-admin/admin.php(259): do_action()

#12 {main}

  thrown

Besides that, there is a jquery error when trying to change the form settings. The menu links on the left side wont work. If we revert back to PHP 7.4.3, everything works as it should. Appreciate any help, thank you in advance. Chris