Reminders (builtin to iOS)
Free with Office 365 / Microsoft account. Decent desktop & mobile apps too and integration into Outlook/Teams. API available via the Microsoft Graph and integration with PowerAutomate if you want IFTTT/Zapier-like functionality.
https://learn.microsoft.com/en-us/graph/api/resources/todo-o...
What's this one missing?
TickTick also has markdown notes and a calendar. I use the notes probably as much as lists, which fit desktop usecase better. Lists could be fine if it was mobile only but still annoying.
I highly doubt that. It's just they are the type of apps no one knows about because a developer will throw a TODO app together over a weekend then not support, market it, or abandon the server after a couple years. As I personally experienced at least twice over the years.
If you ask GPT they recommend these that fit the criteria (among quite a few others):
https://2doli.st/ <- this was on HN a year ago with the same headline https://news.ycombinator.com/item?id=38091771