I mistakenly sent ETH from my online wallet to my ETC hardware (Ledger Nano S) wallet address. Is there any possibility of recovery? And if yes, how?
Thanks and kindest regards
A Ledger device uses a Hierarchical, Deterministic (HD) addressing scheme, where different "branches" of addresses are generated from one seed. It uses one "branch" for ETH, and a different "branch" for ETC, and doesn't expect to find the one in the other (which is why the coins aren't showing up in the wallet UI for you).
So, your coins are likely safe, and you just need to use a HD-browsing tool like MyEtherWallet to find them.
Head over to https://www.myetherwallet.com/#send-transaction and make sure that in the upper-right, you have an ETH network selected (since that's the currency you're looking for).
Choose the Ledger Nano S option for accessing your wallet, and in the top half of the popup that opens, choose the "Ledger (ETC)" option (the
m/44'/60'/160720'/0' branch). In the lower half of the dialog, look for the address you sent the ETH to (it should show that it has some ETH balance there). If you don't see it, click the "More addresses" link to scan forward in that branch.
Once you've found it, select it and click "Unlock your wallet", and you can use the form it pulls up to send the coins to the proper address.