She watched the documentary three times, but she couldn't understand it.
→ Despite watching the documentary three times, she couldn't understand it.

Although they said that the film was a tragedy, it didn't have a sad ending.
→ Although the film was described as a tragedy, it did not have a sad ending.

The leading actor was famous. However, his performance in the film was poor.
→ The leading actor, who was famous, gave a poor performance in the film.

Though
→ Though the leading actor was famous, his performance in the film was poor.

I tried my best, but I couldn't win the leading role in the play.
→ Despite trying my best, I couldn't win the leading role in the play.

The film failed because they invested too little money into it.
→ The film failed due to the insufficient investment of money.

They invested
→ They invested too little money, which caused the film to fail.