Honestly, having any of these vulnerable devices on your network is exposing your whole network, assuming the network is connected to the web.
Your best off using either a separate network for your smart devices with its own router, or setting up a vlan to keep your smart appliances and actual computers separate.
Look, I’ll be honest with you, I’ve never built a dehumidifier (I’m sure you’re shocked). I don’t know what exact components tend to be used. What I do know is that I have a fairly new dehumidifier and we have another one from probably the early 80s. Somehow they both work. Again, I’m not sure what components were used in the older model, but given the age I’d be very surprised if the electronics it uses would be more expensive to manufacture than the newer one.
Really, I think the idea I’m trying to get across is just that you can always aim lower. Sometimes the goal isn’t achieving perfect precision, but rather achieving something good enough. Take toasters for example, most toasters don’t have a timer at all. They have a little piece of metal almost touching a contact. When you turn the toaster on, that metal heats up and it bends until it touches that contact, ding toast is done. And when you turn the little dial from light to dark it just moves that piece of metal slightly further from the contact. My point is, it’s not exact, it won’t be the same on every toaster, and it will probably shift over time. It’s a low tech solution for something that could absolutely be done in a more modern, more precise, and still inexpensive way (a simple timer). But it’s cheaper and simpler to just do it the old way, and for many applications, that’s fine.
Hell, I’m certain there are dehumidifiers on the market that don’t have any kind of humidity sensor at all. Even simpler…