Here's some tips for understanding why some webinars do not appear in the list of embed options:
To embed a webinar, the content must be set to 'Public webcast' within 'Edit Booking'.
Additionally, you may need to change the publish settings from within "Edit Booking" to "Published"
After that is done you will be able to find the embed code for this webinar.
Please see below for further information on embedding content: