Note: Keplr users who log in with Google credentials (via Web3Auth) will receive a private key.
Open your Keplr extension and click on the profile icon in the upper-right corner.
Next, click the three dots next to your selected account, then choose [View Private Key] from the drop-down menu. If the account was imported with a recovery phrase, you will only see [View Recovery Phrase]. For accounts created or imported with Google login, only [View Private Key] will be available.
Confirm by inputting the password.
Once the key is shown, you can copy as needed.