Some hints for programming....

256 step pwm is standard on most arduinos. If you don't need higher resolution, there's no need to get into that low level timer stuff that I got into for the solenoid valve.

Timer pins come in pairs so I think there's a complimentary pin to the one I'm using for the solenoid that also has high resolution on the xiao. I'll eventually write some code and scope it and check.

I think you can plug an air pump into a solenoid controller to check if it can support the additional resolution. We should ultimately build these changes strollers with the ability to use the most resolution they have available even if it's not necessary in order to future proof the hardware.

I think a package with controller and air pump in one and plugs on that package for a solenoid and display would be an interesting design. The bmp280 might even be included in that package or it could be remote with the solenoid.