I found the issue. The issue is with Advanced Custom Fields(ACF). update_post_meta did not work for this field. ACF wanted me to reference the field by ID rather than title and to use update_field function. I know that talking about ACF here is frowned upon so feel free to take this question down.
Their documentation said something like ‘When saving a value to a field for the FIRST TIME (instead of updating), use the field ID instead of the name.
https://www.advancedcustomfields.com/resources/update_field/
My new code looks like this:
update_field('field_637e33286981a', $embed_video, $film1);
Hopefully this will help someone who is struggling with this problem!
PS. I suggest to future me and to all other people to create your own meta fields and register them in a plugin or in functions.php rather than use ACF. ACF seems easy to use but creates lots of problems due to how complicated it is to be easy. YMMV.