GPT-5.2 and GPT-5.3-Codex have been sunset in Codex with ChatGPT subscriptions

It is removed from ChatGPT accounts, and only available through API. AKA this means that using codex 5.3 directly with your ChatGPT account whether on plus or pro plan won’t work, and it can only be used through 3rd party apps, such as your mentioned “Cursor” or “Copilot” because those use the API directly with tokens you buy from them, not with your ChatGPT account.