I’m not a fan of their MacOS based products, but I prefer iOS for the fact that I can rely on getting timely updates. For a good long while. That is not something that is generally true with Android. I’m fine with paying for that level of support.
Last time I looked, no Android vendors provided close to the same level of support.
That said, if I was a business and needed to field in house apps to mobile devices, everyone would be getting an Android device. Custom apps for iOS are a pain in the ass.
Personally I use Nextcloud, but as you want local only, I have used Thunderbird. It’s fine. Cross platform, open source, remote to local sync. Basically, it ticks all the boxes for a calendar/agenda.
You might also take a look at this list: https://github.com/awesome-selfhosted/awesome-selfhosted#calendar--contacts