The cover letter is very much alive, and is just as important, if not more so, than your resume.
Most companies require you to submit or upload a cover letter as part of the application process, and they will check to make sure you have included one before they process your application at all.
Many employers will reject you outright for not doing what was asked. Their thinking is that if you can’t follow a simple instruction in the application process, they will not trust you working with their clients.
Additionally, the cover letter is an important factor in the hiring decision for many hiring managers. To maximize your chances of getting an interview, always include a cover letter with your application.