Just ensure you write down the 24 word mnemonic seed passwords/phrase in a secure location when prompted to do so (and create an on-chain wallet first *and then* create a Lightning Wallet)
In BlueWallet, you can create a LN wallet without creating an on-chain wallet. The LN-wallet uses a different backup system.
Here's a BlueWallet LN backup holding 100 sats:
lndhub://667c9c47fa0ac23c2844:11c65745b9b050dd731b
First one to restore this backup can move it to his own wallet.
Warning: don't use this wallet to receive funds, it's obviously compromised.