For now, head to https://polygonscan.com, scroll to the end of the page and click ‘Add Polygon Network’.
Ppen WETH on Polygonscan.com below, click the three dots on top right at the Profile Summary, and select ‘Add Token to Web3 Wallet’: https://polygonscan.com/token/0x7ceb23fd6bc0add59e62ac25578270cff1b9f619
Verify the address correct, as there are ‘scam’ WETH addresses. It should start with 0x 7 c e b and have > 150 million transfers.
(Or you can just follow the How to sell NFTs on OpenSea guides.)