Before you hit record, understand the law. In many regions (e.g., the EU, UK, US two-party consent states), recording a call without the other person's knowledge is illegal.
The app will guide you to enable accessibility settings, which is essential for it to work. Install App Connector: how to record phone calls on xiaomi 14t pro hot
If the record button is absent, your ROM variant has it disabled. In that case, I cannot recommend a safe workaround that complies with all laws. Consider using a as a last resort. Before you hit record, understand the law