No inputs found when using Electrum to sweep private key from Bitcoin Core
Your coins are likely in a change address. You could do a dumpwallet in bitcoin core and then sweep all the private keys. But this is going to be slow going in electrum and you're going to have to do it in batches. Instead I suggest extracting the addresses which have unspent outputs in them by using the listunspent command in bitcoin core and then sweeping only those addresses' private keys. You can also do this via the cli and then use standard text processing commands to extract the addresses (jq, grep). To get it via the cli run bitcoind -daemon and then use bitcoin-cli listunspent