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FYI - I couldn't add images ie. within image slider and found out that a table for h5p was missing.
See Solution: https://h5p.org/comment/10720#comment-10720
CREATE TABLE wp_h5p_tmpfiles (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
path VARCHAR(255) NOT NULL,
created_at INT UNSIGNED NOT NULL,
PRIMARY KEY (id),
KEY created_at (created_at)
);
Adding it (via phpmyadmin for mysql within the opigno database) solved it for me.