How can I create an ahnentafel?
You'll need to use one of the 3rd party programs such as Family Tree Maker, Legacy, or RootsMagic to download a GEDCOM and create the ahnentafel. https://grms.my.site.com/solutionsgallery/s/
I see that Family Search has a program GEDCOM 7.0. I don't see away to download the program.
Yes, that is the latest standard, but you can't use it to download your branch from the FSFT. You will need one of the 3rd-party programs.
another third party program in Ancestral Quest .... works well for what I think you want to do.