There were so many interesting complicated solutions for different technical problems... that these days are just all replaced with "it has an esp32 and small touchscreen"
Which is great, in a way. It makes it easy to solve a lot of problems.
"how do I control the fan in my room?"
"the power outlet is on the wifi and you can send it a HTTPS request from an app"
That's simple and powerful and cheap... But it's not really all that interesting, since so many things get solved the same way.
How does my thermostat work? Is it a bimetallic strip and a mercury tilt-switch, combined with a clever rotational temperature setting mechanism that adjusts the activation point of the switch?
No... It's a little microcontroller running Linux that's connected to the wifi and has a touchscreen.
How's it different from my smart outlet or my router or my mouse or my smart soldering iron or my watch?
It's got different sensors and different relays. That's about it.
And sure, there's a lot of cool no applications enabled by the fact that it only costs like 10-20$ to embed a Linux computer with a touchscreen and a wifi connection into anything. There's a lot of stuff that was simply impossible to build (at least at a reasonable price) a decade or two ago.
But those things we're building are just less interesting, internally.
What's inside this smart device?
Oh, it's an ARM chip, a wifi/Bluetooth module, and a little LVDS LCD.
What a surprise.
The other day I pulled an LCD module off a smart woodworking power tool and plugged it into a portable gaming system. It worked perfectly. I didn't need any adapters.