Hi @TheoMolenaar, this was fixed in Backlight 4 in late 2021. Can you check that you have the latest version of the modules in the Backlight Modules page? If you do, can you visit Designer > Templates, click on the name of the WP template and then click on Export Theme to Wordpress?
If that still doesn’t solve the issue, try to edit the exported file itself. Line 145 of wp-content/themes/BacklightWordpressTheme/inc/theme_posts.php should look like:
if (is_admin()) {
(note the parentheses in is_admin(), which were missing prior to the fix)