You would need 3 things to accomplish this:

1. A way to periodically / automatically export your calendar(s) as ICS - this add-on used to do it, but it's not compatible with recent Thunderbird versions. I suppose you could do this manually.
2. A way to get this file on your phone periodically/automatically. This can also be done manually.
3. An Android app to import this in your phone calendar. It seems Calendar Import-Export can do this.

The alternative would be to use a CalDAV server. By default Lightning supports the CalDAV internet standard. You would need an account on a CalDAV server first, then on Android there are a few apps that support CalDAV sync. Please open a separate question for this if you want more information.

Hello Fabián, thank you for answering. The short answer would have been: No there isn't. At the moment I am using Outlook and am syncing that with Android Sync to Business Calendar. That works nice and easy and, most importantly, without any Google interference. But since I am trying to switch to open source as far as possible, I have to try and find solutions for several things and this is one. Regards,

Wim

Hello Wim.

The shorter answer would have been to ignore you. I predict this will happen a lot to you based on the response you wrote.

I encourage you to research your assumption that the app you installed via Google Play works w/o any "Google interference".

Good luck in your research, if I can suggest a good resource to start getting rid of Google in your digital life, this would be it.

Hello Fabián,

judging by your reaction: I hope are not insulted in any way? That was not in any way intended. If I had answered the shorter way, I would certainly subsequently have given the arguments as to why I said that. And regarding my assumption: perhaps it is naïve but I do indeed assume an app not written by Google or one of their associated companies to be Google free. And considering that the syncing process is done via usb does indeed make me assume Google can not in any way reach my calendar data. The only thing is I have to do it by hand, but if that is the price of prying myself lose from Google, so be it. But then on other hand: Google has indeed developed into a very intelligent sort of squid... I have indeed started getting rid of Google and looking at the comparison table in https://degooglisons-internet.org/en/ I have discovered quite a number already. Thanks for the link by the way. As to why I reacted the way I did: I have indeed learned quite a bit already, but when someone starts using WebDAV and CalDAV it goes over my head if only because these are constructions I do not see myself using in my own home, despite the fact that I have this Synology NAS which is quite capable of providing me with my own private cloud. Regards,

Wim

Our writing lacks context and expression, I'll blame that for my interpretation on the way you answered. All the better if it was not intended, keep in mind others won't explain/reply similarly.

Regarding "apps not written by Google", most (if not all) include many libraries for debugging, tracking, geolocating, online sync, push notifications, backups etc.

This link may explain better than me why the lack of Freedom affects your privacy on many levels that can't be just solved by using different apps (although that's a very good first step).

You have to take into account the operating system, the drivers, the libraries, the hardware, the app store (Google Play), etc. and find alternatives for all of that.

It does that doesn't it? Lack content and expression all the more since my mastery of the English/American language may adequate, even more than that, but I am, alas, not a native speaker and what is a native speaker, considering the size of a country like the USA.... Regarding Google: I am using Thunderbird and Firefox on my pc and Firefox Focus on my Phone, a Nokia 6 by the way. The standard search engine is DuckDuckGo on my pc as well as on my phone. On my pc I use an off line id and Saas as MS puts it fills me the deepest mistrust. So, although I use an MS Office version, 2010 en 2013 to be precise, the use of any cloud-service other than my own abhors me. I have been using Libre Office, but then my calendar-problem still defeats me, as you know... I am, at the moment experimenting with Linux OS's like Mint and Ubuntu as well on a server as well as on the desktop. It takes some learning... I stiil have this One Plus One on which I tried to install Lineage, but that did not work. The cause I'm still puzzling on. May be worth a question on some other forum? So, I am trying to degoogle....

Wim