Electrum's export transaction after version 4.0.1 are all PSBT
But you must be talking about 'binary PSBT' export: the "
transaction.psbt" file that the desktop version can export.
Does this maybe just work with a Windows/Mac version of Electrum and not with the Android version?
AFAIK, currently the android version can only export the PSBT as text in base64 format or QR code, there's no binary option.
I'll explore a bit more and update you if I found any option to export it as binary.