It is incredibly worrying that this post is not gaining any more traction on HN, which I presume is due to the innocuously appearing title. A more fitting headline would be "Notability Implements Subscription Model, Limits Editing Starting Nov 2022 for Current Users", which, while a very disrespectful move to the current userbase that has paid for this program believing that they'll be able to use its basic features forever, is also actively against the App Store guidelines [1]. This is a perfect example of what is wrong with the current state of affairs regarding the App Store.

The App Store does not allow users to download previous versions of an app (for laypersons, that is; all versions of an app are usually still hosted on Apple's servers, but even users with an interest in tech will have to jump through a lot of hoops to download an old version of a bought app), which means that users will be barred from functionality they paid for and not be able to keep using the version of the app they bought (which makes the usual argument brought up every time people debate that companies have to switch to SaaS, because of costs incurred by developing updates, moot).

Is it such a ridiculous opinion to assume that, if I buy a paid app without in-app purchases, I will be able to keep using the existing functionality forever (or as long as no os update breaks that version, at the very least)?

[1] Taken from Reddit, as afaik there is no public version available:

Apple's guidelines, 3.1.2(a) state:

If you are changing your existing app to a subscription-based business model, you should not take away the primary functionality existing users have already paid for. For example, let customers who have already purchased a “full game unlock” continue to access the full game after you introduce a subscription model for new customers.