The Deck’s Wi-Fi chip (Realtek or Intel depending on model) can get saturated. Set → Download & Connections → Max simultaneous downloads to 2-3. Avoid 10+ parallel downloads, as they can cause packet loss and slowdowns.
Disable IPv6 in JDownloader (Settings → Advanced Settings → search for ipv6 → disable). Also, toggle Wi-Fi power saving off in SteamOS Developer settings. jdownloader steam deck
Launch the Discover Software Center (blue shopping bag icon in the taskbar). The Deck’s Wi-Fi chip (Realtek or Intel depending
Enter your sudo password when prompted. Confirm the installation. " add /run/media/mmcblk0p1 as "Other files."
Open Flatseal → Find JDownloader → Under "Filesystem," add /run/media/mmcblk0p1 as "Other files."