The principle purpose of a cover letter is to get the employer to review your resume and spark interest in interviewing you for a position. It is also a writing sample, a testament to your writing capabilities. Like the resume, cover letters are used to convince the reader you would be a good candidate for a position within their organization. You should work to tailor each cover letter to the specific position, incorporating language from the job description and highlighting the experiences you have that match the specific position. In addition, if you are not yet applying for a job but instead inquiring about a position such as an internship, you may find this is template example useful.
What about using ChatGPT? - This is a great tool to create a starting outline for a cover letter (which can significantly cut down on time!), but a drawback can be that even at its best it tends to just reiterate your resume. Cover letters are a place for you to show your excitement and include some specific details, which cannot often be perceived by ChatGPT. This article from Forage may be helpful in discerning how you want to use ChatGPT to your advantage, as well as this article from WSU with some classic do's and don't.