I now read everything with https://bazqux.com (the most true-to-Google Reader I found and the only SaaS I pay for, no affiliation) and it's really enjoyable. The RSS reader format is definitely one of the best reading formats in my opinion.
I've been using Feedly for a while (since Google Reader went away) and it works well. I'm on the 'free' tier and am happy with it. Note: I'm not associated with Feedly directly (not an employee, not paid by them, etc)
Seems like a weird move for a company focused on newsletters.
I could see why they would want Substack readers subscribed to multiple publications to have one place outside their inbox to get more value. Some people don’t actually like the email newsletter format and words are words wherever they are.
An RSS reader makes perfect sense for them, actually.
That combined with kill-the-newsletter (for turning email into RSS feeds) has been working really well for me for the past year or so.