Столкнулся с проблемой: платка Arduino Nano v4.0 в среде Arduino IDE 2.3.5 прошивается нормально, если выбрать в меню Tools -> Processor: "ATmega328P (Old Bootloader)". Но в среде VScode PlatformIO прошивка не работает.

Загрузчик не отвечает, в консоли терминала видны ошибки:

...
Configuring upload protocol...
AVAILABLE: arduino
CURRENT: upload_protocol = arduino
Looking for upload port...
Auto-detected: COM10
Uploading .pio\build\miniatmega328\firmware.hex
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xe8
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0xe8
...

Как исправить: откройте файл platformio.ini и добавьте туда строчку upload_speed = 57600:

; PlatformIO Project Configuration File
;
;   Build options: build flags, source filter
;   Upload options: custom upload port, speed and extra flags
;   Library options: dependencies, extra library storages
;   Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html

[env:miniatmega328]
platform = atmelavr
board = miniatmega328
framework = arduino
lib_deps = 
   adafruit/Adafruit Si5351 Library@^1.4.2
   milesburton/DallasTemperature@^4.0.4
upload_speed = 57600

[Ссылки]

1. PlatformIO upload options site:docs.platformio.org.