Syncthing.
I also will make a copy on a usb drive if I’m traveling and keep it in my luggage. Lesson I learned when I broke my phone during a recent trip and didn’t have any way to add a new device to syncthing to retrieve my keepass database. Which was a real pain in the ass.
I don’t use iOS, so I can’t speak to it directly, but some quick searching tells me it supports IMAP, caldav, and carddav. If so, you could just use native apps.
Most of the privacy respecting email services require a paid plan for this, but they are inexpensive.
This doesn’t solve your Google calendar ask, but I pointedly don’t have my work calendar on my phone. I just check each calendar separately when needed, it’s not much extra work.
I would say the majority of objections to systemd pertain to perceived overreaches of the project (perceptions I generally share). So in that sense, it is kind of on brand.