The content of the letter isn’t super important–just show your voice and give the audience (hiring manager/HR) a feel for who you are as a person. The quicker you can become real, the better chance you have of getting through the noise.

If you are less experienced, talk about what you’ve done and how it will transfer to the role you want. If the role is junior or mid, the manager is probably expecting people coming from other fields. I’m open to this myself, but everyone has different criteria.