In another thread you wrote:
Learning to use netclasses properly is a skill worth learning in KiCad. It does take a bit of time to setup, but after that selecting track width is mostly automatic. A net class is a set of rules for track width and clearance and you can set up a few of them. For example start with 2. The Default Netclass which you use for almost anything, and a Power Netclass you have to add. Then you can set up this Power Netclass to use for example 1mm wide tracks to distribute some power across your PCB. In the schematic, you make a list with nets that belong to the Power Netclass, and after that, whenever you start routing on the PCB, the track width and clearance will be automatically adjusted according to the netclass of the track you are routing.
Also, netclasses just set up the defaults for the nets. If you for example need a track going to an I2C pullup resistor, then you can still use a thin track even though it is a part of the (pesumably wide) “power netclass”.