I do this with emails. ADHD not austism. I’ll throw this out as a suggestion:
Amazon, for its many faults, has a distinct and effective approach to writing. Put a short summary/objective paragraph at the top, detail needs/design/whatever, alternatives, whatever supporting information in an appendix, and give everything headers so you can easily find what you want. The idea is to make it pyramid shaped: the important information right at the beginning and more detail the further you go down. Someone reading it can just stop reading when they need to.
I’ve seen documents that are like 10 pages of ‘real’ content and a couple hundred appendix pages. I wouldn’t go to this extreme in personal communication, but might help realize what needs to be kept or not.
Also bullet points are fine. It baffles me they aren’t considered ‘real’ writing.
Send your thanks directly to the maintainer (preferably email/mastadon/twitter/etc, not a ticket)! Open source maintainers don’t get a lot of positive direct feedback.