Hi everyone, the error described in the tittle is given in the Manjaro Linux platform (Manjaro 21.0 with KDE Plasma 5.21).
This happens when I try to download a global theme on System Settings, I noted a consult at the Manjaro forum related to this problem but for far no clues about it.

I have absolutely no problems with my internet connection nor the speed (200/200Mbps) and the problem happens no matter if Ethernet or Wifi connection.

Thanks in advance for helping me.

Hey mate, cheers.. I'm also having the same problem since yesterday. I am in Arch. Only fonts can be downloaded or may I say, only in the fonts it doesn't say connection error.
Besides there, in all places, I am getting that error.