I don't have time to give p2pool the ability to parse the new address format right now. Old addresses still work. Internally, Bitcoin (Cash) software converts the address format into a public key, and the pubkey is what is encoded in the transactions. The pubkeys have not changed.

If you tell p2pool to mine to an old-style p2pkh address and are using a wallet that only supports CashAddr addresses, you can use https://cashaddr.bitcoincash.org/ to convert between them.

If someone is able to add CashAddr support in a pull request, I would be most appreciative.