Set post title based on custom field with new (Gutenberg) editor

With the old WordPress editor it was possible to set a custom post’s title to a custom valued based on another custom field by using the wp_insert_post_data filter. This is described here for instance: https://wordpress.stackexchange.com/a/198268/26545 However, with the new Gutenberg editor, this doesn’t work anymore (at least for me). I have read that the Gutenberg…

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