I use the app opentask. Based on your criteria, it’s exactly what you’re looking for. It’s all stored locally on your phone, it has the ability to set recurring tasks, and you can create categories of preset and custom tasks. Deadlines can be set as far into the future as you need, down to the minute. It’s available on F-Droid.
I know some of the union leaders at UPW, including one of the Paizo writers that may have worked on the starter adventure (I don’t know for certain). They’re incredibly passionate about their work, and honestly would understand your frustrations about capitalism. They likely pushed to make as much as possible free, so folks in your position would still be able to share the joy of their work even if they can’t afford the starter adventure.
I know none of this will make your frustration go away, but I hope you know that they didn’t do it out of malice.