Prior to OA, the ability to use the account creation functionality on mainnet was restricted. With OA, those restrictions have been lifted. There is therefore no longer a need to go through the Hedera Portal to create an account.
However only someone with an account can create an additional account. An existing account with a sufficient balance of hbars will submit and pay for the transaction that creates the new account and fund the initial balance. The transaction creating the new account will include the public key to be associated with that new account and that account's identifier will be made available in the receipt for that transaction.
Account creation may or may not be subject to KYC depending on the third party creating the account and applicable regulations.