A very popular and favoured feature of google is the possibility to easily synchronize all your devices. The downside is that for all those "free features" you don't have to pay with cash, but you pay with your data.
Here we suggest a possibility how to bypass google and still easily synchronize all your devices.
One way is to use Nextcloud, here you can sign up and get a cloud hosted e.g. in Germany with up to 5GB for free. There you can store all your data without concern. If you want even more security, you can even host your own cloud-server with Nextcloud.
If you want to synchronize your calendar through your devices, first download the Nextcloud app. Now you only have to install DAVx⁵ from the F-Droid store which helps you to sync your calendar and contacts (for further informations see here).
If you don't want to use Nextcloud, you can use FOSS (Free and open-source) apps like Simple Mobile Tools or Etar. Both apps are available in the F-Droid Store and can also be synchronized with the help of DAVx⁵.