You do not need to generate 1 million addresses using Electrum.
You could've simply used the Iancoleman website or a Python library to generate only the 1,000,001st address, and then import its private key into Electrum.
Addresses don't have to be generated sequentially.
He can do it just on Electrum. BitMaxz explained it and I tried it on desktop Electrum and it worked.
Make use of the
command using the console on Electrum is all that is needed. It takes less than 30 seconds.