Unity is behind "Pretty much half of all games " on all platforms [1] I suppose it's possible there have been 100K Unity games written if you include abandoned efforts, education etc. No idea of mean LOC but that multiplies out to a lot.

Also Xamarin which if I read this [2] correctly owns a third of the mobile app market. I don't know whether that's credible but apps are a huge market.

It is possibly that could get you the 10 bn. It is quite certain that there has been more than 10 bn lines written on.NET Framework, probably far more, as for 15+ years it has been the dominant language for corporate apps built on the Microsoft stack.

On top of that.NET Core is growing much faster over time,according to their blogs, and it's cross platform as you know.

[1] https://www.google.com/amp/s/techcrunch.com/2018/09/05/unity...

[2] https://www.datanyze.com/market-share/madp/xamarin-market-sh...