I work in a fully remote organization. I _always_ read cover letters. I have wasted too many years of my life trying to decipher some ungodly pile of crap somebody thought was a question (much less a spec!) and a cover letter can be an indication of a candidate's writing ability.

Poor writing leads to wasted hours, wasted sprints, and frustration. Good writing shines a light on incomplete reasoning and logical inconsistencies. A person who takes the time to write a decent spec is the person who has considered "what, exactly, do I want?" in detail. Too often people try to paper over their complete inability to write a paragraph by saying "let's get on Zoom" and spewing out nonsense verbally, because this is somehow better than putting nonsense in writing.

Unfortunately, if the person reviewing your application is a terrible writer - and most are - it's unlikely your cover letter will be read.