After installation of flatpak from PPM (Puppy Package Manager) it is necessary, to install "policykit-1 from PPM, to get flatpak working. Afterwards write into console one of the following two commands:
1) flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
2) flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
to be connected to flatpak database. Then restart F96-CE.
Beware, that the console command "flatpak search ..." doesn't work on F96-CE_4. You can search on the flathub web site for a package (program) and then install (with a console command) according to the information there.
I have done the installtion of flatpak with F96-CE_4 and flatpak 1.6.5.