The electrum install to USB is messy and instructions are inaccurate. Running the electrum-4.5.5-x86_64.AppImage on the host computer doesn't install to the USB.
A prompt window says Electrum wallet -> Wallet: default_wallet -> Choose... -> choose the USB path /media/hostComputerUsername/USB -> File name: there are no files, so the Open button is faded out?
What Electrum wallet version you used excactly?
There is install version for wind0ws, than Standalone and Portable version (be careful with portable version).
I would recommend switching to LinuxOS and using Electrum Appimage that works without installation.