The issue is, that PLL_PREFIX . 'block-editor-plugin' doesn't exists until you are on the edit screen with the block editor active (and Polylang Pro installed).
The fix would be to enqueue the script only when AdminExtension::isEditPostScreen() and WP_Screen::is_block_editor() is true.
Currently, when visiting wp-admin/edit.php with Query Monitor active, you get this warning:
The script gets enqueued in https://github.com/Supertext/polylang-supertext/blob/5ff2a8eb9240c3e6a2bc38f9b1183030ee8768fc/src/Supertext/Polylang/Backend/AdminExtension.php#L124 and is registered in https://github.com/Supertext/polylang-supertext/blob/5ff2a8eb9240c3e6a2bc38f9b1183030ee8768fc/src/Supertext/Polylang/Core.php#L150
The issue is, that
PLL_PREFIX . 'block-editor-plugin'
doesn't exists until you are on the edit screen with the block editor active (and Polylang Pro installed).The fix would be to enqueue the script only when
AdminExtension::isEditPostScreen()
andWP_Screen::is_block_editor()
is true.