Thank you for raising this. My subscription was up for renewal next year, and I think I'll look elsewhere now.
The only reason I chose to support S Notes in the first place is they were the best designed FOSS notes app at the time, and 4 years later they have plenty of competition in that space fortunately. Honestly I expected better from them, they say all the right things but I guess the greed just got too much for them.
Even if what they're doing is legal, it still has a negative impact on the privacy community. F-droid no longer providing Standard Notes builds is going to cut off people from using this app's updates going forward. It may end up being relegated to the IzzyOnDroid repo, but still not everyone uses that.
At least Signal provides a method outside of F-droid for automatic updates.
I believe you're looking for Easer, though not sure how well it matches to your criteria https://github.com/renyuneyun/Easer https://www.f-droid.org/en/packages/ryey.easer/
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