My newsletters, like anything I want to read, go to Readwise Reader. However, I don’t subscribe to them directly with my Readwise address, but have created an email address along the lines of news@mydomain.tld, which forwards to Readwise. That way, if I ever use another app for reading, I don’t have to change all the subscriptions.
When I was subbed to a lot of newsletters, I moved to this exact setup and loved it. I now have less newsletters to read so I now use Reader for them.
The only minor downside of Reeder for me was not being able to delete newsletter editions that I read and didn’t need to see again.