"Legacy" (aka P2PKH), starts with a "1"
"Legacy P2SH" (aka P2SH), starts with a "3"
"SegWit P2SH" (aka P2WPKH-P2SH) also starts with a "3"
"Native SegWit" (aka P2WPKH), starts with "bc1"
If you don't specify which address type, I believe Electrum defaults to "Legacy" and imports your private key as P2PKH.