Do people develop python in Windows? is there any distinct advantage? example: the pi costs $30 and a used keyboard/monitor from a pawn shop, but anything with windows is way more expensive.
Yes there are some advantages, but those aren’t Windows specific. The advantages also apply to traditional desktops/laptops running MacOS or Linux. There are tools written for those platforms that won’t be available on the pi, although the raspberry pi ecosystem is rich enough that that won’t matter much. There’s also the specs of the machine. A beefier machine can power multiple monitors that can let you see more code at a time. That’s just surface level. We can chat more if you’re interested.
Having said that, sounds like what you have right now is working for you. There’s no need to switch to something else if you’re making progress. It’s pretty cool that you got started this way. I wasn’t aware that python is used by car mechanics.
If the pi works for you compared with buying a much more expensive rig, that's great. I was pretty impressed with the desktop experience on the Pi. But if you already have a more expensive computer, developing on the pi doesn't give any advantages. It's slow, it doesn't have much memory, it's storage is SD cards (both slow and prone to failure). Now deploying the result on the pi is great (you can put those anywhere, they're low power, etc).
If you are looking solely at Python software development, a faster, more reliable machine is always helpful, but some may prefer Linux or MacOS over Windows. All that said, the Pi is a great way to break into software development at a low cost.