No errors or output from the add?
I don't see anything wrong in what you are doing assuming you have permissions but if it's just for your user you can flatpak --user to install in your homedir instead of system-wide.
Also convenient for distro-hoppers as you can just share or copy the flatpak dirs between home directories so you don't even have to redownload for every reinstall.
I'm involved with people organizing free rave parties of all sizes and production grades and it's something I hold dear so your analogy hits close to home!
They all have income streams from outside the scene, including the ones responsible for events with thousands of attendants. While there are countless stories of people making industry connections promoting their careers and getting work there, a DJ or producer expecting they will be able to sustain a professional career purely through scene exposure or free parties is delusional.
That a few have been fortunate and resourceful enough to do so for a while is great but it's not an indictement of the scene if one of them makes a "The Scene Is Dead" post on Instagram that they're tired of the freeloaders and only doing paid gigs from now on.
Agreed in the mobbing of the wider thread but I hope you don't see that going on here?