Flatpak on Xperia 10 II - Aarch64

Is it possible to install 64bit Flatpak Support for Aarch64 Devices such as the Xperia 10 II following the instructions on GitHub - sailfishos-flatpak/main: Documentation and issues and simply replace the command to add the repository by
devel-su ssu addrepo rinigus-flatpak http://repo.merproject.org/obs/home:/rinigus:/flatpak/sailfish_latest_aarch64/aarch64/

as rinigus seems to has provided a version for aarch64?
I do not understand what the tbuilder from GitHub - sailfishos-flatpak/tbuilder-project: TBuilder project is for. Why couldn’t I simply use the command
devel-su pkcon install flatpak-runner
?
Has anybody tried to install 64bit flatpak apps?