I've had a few issues with the discover store only working sporadicly in desktop mode amd when looking it up found ne good solutions that don't require a system restart or work reliably.

The error I had was something along the lines of a lost connection due to a refused TSL-Handshake these are the errors I get trying to refresh the available updates for example:

I press update All and get:

no metadata URIs for vendor-directory

I press it again:

the application [...]/x86_64/stable requires the runtime org.kde.Platform/x86_64/6.4 which was not found

and again:

aborted due to failure (While pulling runtime/org.kde.Platform.Locale/x86_64/6.4 from remote flathub: Peer failed to perform TLS handshake: Error recieving data: Connection reset by peer)

I would love it if anyone can help me with this as I would like to be able to reliably update my packages (and install new ones which often jeilds the same errors)

I have tried installing over the terminal, which results in the same errors. I have tried it on different Networks. I have restartes flatpak-sytem-helper. service as well as wpa_suppclient.service I have tried flatpack repair. Restarts of the whole system work occasionally but not reliably.