Something I've found useful is adding flatpak support to the KDE Discover store.
To install Flatpak support in KDE Discover, you need to install the Flatpak backend package. For Ubuntu-based distributions, you can run sudo apt install plasma-discover-backend-flatpak. After installation, restart your system and add the Flathub repository using flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
Do you think the USB SSD issue could be because of the partition format? Example, Windows NTFS support can be enabled on Linux so you can then mount it. You can check partition type using a tool like
fdisk -l. Perhaps that might help.