Sorry about the inconvenience. We’ll look into the Opensea issue separately. One reason why you couldn’t restore your seed phrase on Metamask could be that you’re using legacy Brave seeds (typically 24 words). Regardless, please follow these steps to obtain your account’s private key.
Step 1
Navigate to the desired account under Accounts.
Step 2
Click on the Edit button as shown in the screenshot below.
Step 3
In the modal that appears, click on Private key and then Show key.