@ErosBlog Glad to see open-source, local apps getting a mention here! Because that's really the only solution. If it's supported by ads, they have your data because they're using it to target the ads. If they have your data, it doesn't matter if they turn that data over willingly, they could also be compelled to by a court. Doesn't matter if the app asks for your state either, that's easy enough to figure out if you aren't using a VPN all the time (and even that wouldn't be a guarantee.)
And if it's not open source...you have no idea if they're collecting your data or not. If it's ad-supported the data collection is pretty much guaranteed (well, *someone* has your data if not them)...but even if it's paid and/or ad-free, a lot of devs will harvest all your data for literally no reason just because that's the way they're used to doing things and keeping you safe -- especially *from them* -- isn't often part of the design process.
Also check your device settings to ensure this locally stored data isn't getting backed up to "the cloud"! Google and Apple do have the resources to fight a demand for that data in court...but will they? Will they win? They're not just gonna outright refuse a lawful order. They do turn over data regularly.
Security is always a balance between risk and convenience.
If the risk has substantially changed, then it might be worth reconsidering how you balance that. If you're very worried, maybe even keep the data on paper that you burn as needed. Or on an old phone that you keep offline. Or in a regular calendar or notepad app, possibly in code, using non-obvious event names or something like that. Make it harder to harvest and process in bulk.