I'm upgrading my btc core to v0.18.1. I'd like to export my wallet to electrum. Is it possible while syncing? How?
This guide is intended for users of Bitcoin-Qt who do not want to wait for their wallet to be synchronized with the network, which may take many hours or days depending on the hardware spec. The guide teaches users how to transfer their coins to Electrum bitcoin wallet, which has lower security but a faster startup time.
To answer your question, yes you can. Syncing the blockchain has nothing to do with your private keys. Electrum has a list of blockchain servers to use your keys with immediately.