The framework-arduino-nrf52-mbedos package seems to have been long deleted from the registry. Nowdays, it’s just framework-arduino-mbed (mirrors https://github.com/arduino/ArduinoCore-mbed).
Are you sure can’t port your project to use the latest stable version of the nordicnrf52 platform and the latest ArduinoCore-mbed framework that uses?
If you absolutely need that old version, you can download it from the link, then unpack it somewhere (e.g. C:\Users\user\Desktop\old-framework), then force your platform to use that copy instead of trying to download it from the registry by editing your C:\Users\<user>\.platformio\platforms\nordicnrf52\platform.json, find the lines