microcontroller VS MH-Z19

It depends on the meaning you put into the word “model”. In my opinion the technology (at least the open source ones) is not ready to “model” or simulate both hardware and software at the same time. For hardware, I’d say take a look at CadQuery because you mentioned “large”. Large things require collaboration. Collaboration requires merging work of multiple people. AFAIU That can only be done with CadQuery today. Though CadQuery doesn’t offer a standard way of handling large (and, thus, modular) models. You can check my take on how to use CadQuery for that. For software, you can try VIAM if you feel adventurous. If you don’t want to be a Guinea pig then you may consider using ROS2 though its take on “simulation” is a bit different. If you choose ROS2 and you have some CPU in addition to Arduino’s, you may want to consider my take on controlling Arduino. Though there will be an adventurous aspect to it too. If you don’t have anything in addition to Arduino, you may want to consider micro-ROS instead.

You shouldn’t have to implement such basic building blocks yourself in 2023. Please, consider using https://github.com/openvmp/microcontroller . Unfortunately it’s not yet packaged as an Ubuntu package. So you’ll have to follow instructions to clone it (and it’s dependencies) into your workspace.