To help drive home the privacy angle, you might consider open-sourcing it and also making it available on F-Droid. Also, why does it say "in-app purchases"? If this is a simple calendar I don't see why any purchasable extras should be necessary. (While many in the HN crowd lack the requisite equipment to make use of your project, we do have girlfriends, wives, sisters, and daughters who might benefit from a privacy-r…
In-app purchases: You can buy another theme if you want. There is no need to do that - the whole functionality is available anyway. I thought it would be nice to at least have the opportunity to make some money from it... I haven't thought about open-sourcing it... Maybe I'll think about it...
If you did add a license, users could submit PRs of bug fixes or new features. If you don't have a lot of users it probably would get very little traffic and so not become burdensome. (And you can always ignore it... Not ideal, but life comes first)
If you care about privacy and want to have some fun with the license idea, you can add an Ethical Source license, so anyone who uses your code has to comply with a code of ethics. (https://ethicalsource.dev/licenses/) Maybe a license that says you cannot use this if you actively work against women's reproductive health/freedoms?