Great question — answering as the UphillTech team:
It does seem to improve results to "some extent". Even though our website was already visible in Google AI search mode, 2–3 hours after the file was added to the web root folder, the links off to the side in search showed two pages' URLs: the home page and the contact page, both from Markdown links in our llms.txt .
Full answer by Mehdi: https://webmasters.stackexchange.com/a/148733 (CC BY-SA 4.0).
Need it done for your business? UphillTech.