Especially with the rise of “ghost postings” so quantity over quality is greater than ever these days
I always thought of a cover letter for clarifying something on your resume. Ex: you’re changing careers or industries and out want to clarify why your experience is relevant. So, I don’t do them for every application but in certain situations.
Originally it was to introduce yourself and why you’re sending them a resume in the mail. A really good cover letter will get you past HR send your letter and resume to the hiring team. Thst function has largely been replaced by resume scanning tools.