If the author was concerned about getting censored by Google or feeding their data empire, they could set up a self-hosted Google Docs-like, like NextCloud.
The readers would still need to trust the author's not doing anything nefarious with their IP addresses, but I guess there's a degree of implicit trust when subscribing to a newsletter.
I would just put it on my own server. Are people really worried about clicking a private link and having their IP address logged? Just opening an email with a tracking pixel triggers that already, and you have to assume clicking a link will log your IP whether with Google or Constant Contact or any other mass email provider.
The readers would still need to trust the author's not doing anything nefarious with their IP addresses, but I guess there's a degree of implicit trust when subscribing to a newsletter.