I’ve installed Espressif8266 staging version platform. There is framework-esp8266-nonos-sdk package in it. But the upstream version at GitHub - espressif/ESP8266_NONOS_SDK: ESP8266 nonOS SDK is somewhat newer. Is it possible to use staging version of non-OS SDK too?
Please file an issue here Issues · sanderv32/framework-esp8266-nonos-sdk · GitHub
Also, you can try to replace this line with "version": "https://github.com/espressif/ESP8266_NONOS_SDK.git".
The platform.json is located in %HOMR_DIR%/.platformio/platforms/*/platform.json