We’ve updated the solc-input.json at How to verify a contract on Etherscan/BscScan/PolygonScan , which should now correspond to the latest version of the proxy contracts deployed by the Upgrades plugin.
You’ll need to contact Etherscan as described here https://info.etherscan.com/update-on-similar-match-contract-verification/ and provide the above solc-input.json.