So always make sure to check the transaction and the hardware wallet carefully before you sign the transaction and I suggest you if you have the fake Electrum wallet installed much better uninstall and clean the PC/Laptop and install the original Electrum to keep your wallet safe.
If the fake Electrum clients indeed only generate one large transaction, then uninstalling the fake client should be enough. I haven't seen any reports of the fake clients changing OS settings or running trojans, trying to install other malware or similar behavior. If those things were done then it would certainly require an operating system reinstall, and you'd skip the uninstall because in that case it's not guaranteed the uninstaller will be honest and clean up itself. It could leave a backdoor behind.