If your computer currently has malware on it, it's game over already. They can capture your master password, decrypt your vault, and do all sorts of things even without you exporting a plaintext csv.
If you just don't want plaintext passwords to hit your hard drive, use a RAM disk to write the csv, then encrypt it and save to hard drive, then unmount the RAM disk.
Also, the encrypted export file's format is understood.
See, for example, the parser tool I wrote here:https://github.com/cfbao/lastpass-vault-parser