@Leinth if you are using a Bluetooth OBD-adapter and a mobile app, you could try an app called V-Tool https://v-tool.app/ This app reads codes and live data on the same level as VIDA or Vdash and presents them also in the same code format and is also able to perform lots of service functions, but without the need for a laptop and cables. The only downside is, it currently still lacks support for freeze frame data, which could be problematic when you are chasing temporary errors. But you need a decent adapter that supports highspeed and lowspeed CAN, which is only supported by a few little bit more expensive adapters. Here is a list of tested and recommended adapters https://v-tool.app/supported-obd-adapters/
Your P0420 already gave away that you are not using a Volvo specific scanner, as VIDA and Vdash use a slightly different code format. P0420 would be ECM-P042000 in the Volvo Format.