Try running the following: flatpak remotes --columns=name,url,options
I think the issue is you have one remote installed as a user remote, and the other installed as a system remote. You might need to delete the signal remote and re-add it as a user remote.
Hi there, thanks for the report! Could you paste the output of
uname -aas well? It may be that you are running a 32-bit arm system. This flatpak is only for aarch64, 64-bit arm. I think the default raspberry pi OS was 32-bit arm until rather recently. Fortunately if you're using a Pi 3 or 4, it's actually 64-bit hardware and should be easy to switch over.