Am I sinful for my friend watching clips of unveiled women in a foreign film that I recommended to him, and what is the fundamental rule regarding bearing the sins of others?

It is forbidden to look at what is unlawful regarding women. Therefore, you ought not to have directed your friend to a movie that contains immodestly dressed women, or you should have warned him against looking at them. If you directed him and knew that the movie contained such content, then your friend bears the sin of looking, and you bear the sin of guiding him to what is forbidden, especially since the movie is for entertainment and there is no need for it. Guiding to sin is itself a sin. Therefore, you must advise your friend to stop looking at forbidden things. A believer should preserve their time, as watching movies is a waste of time and rarely free of objectionable content.