I can't flash my new ATMega328p with PL2303 USB-TTL converter
The ATmega328 comes from factory without any boot loader. There are several ways to flash it (either fully or just a bootloader), but UART upload through the RxD and TxD pins isn't one of these.

The simplest way to upload initial software is using the built-in ISP interface through the MISO/MOSI/SCK pins. You need a programmer for that, which may be as simple as some GPIOs from a Raspberry Pi. It's also possible to repurpose an Arduino as the programmer.

Choose your poison, avrdude has to support it, that's the limitation.