The iPad drawing app Procreate has a smoothing tool that sounds kinda like what you're describing—you basically draw a line freehand, and then Procreate smooths

The iPad drawing app Procreate has a smoothing tool that sounds kinda like what you're describing—you basically draw a line freehand, and then Procreate smooths it afterwards. Most other drawing apps (like Clip Studio Paint, which is what I primarily use) have a comparable ability to smooth the lines as you're drawing by stabilizing the actual brush tool—basically slowing down the responsiveness of the brush to reduce jitter.