Chromebooks are commodity computing devices aimed at students & those who don't really need a "real" computer (for surfing the web / checking webmail / watching cat videos on Youtube, a Chromebook works just fine)

However, you can pick up a Chromebook for (at the time of this writing) around $50 shipped that will run linux directly on its hardware. This allows you to run a variety of open source software on the device without worrying if the "brand name" set top box is spying on you or not (and "yes" quite a few of the catchily-named set-top boxes that promise you the world are riddled with all sorts of spy- and malware)

What can you do with a Chromebook running linux?

★ Home media server - this is open source software that does everything the "Firestick/Roku/Chromecast/etc" TV boxes/sticks do, but without the spyware & nagging advertisements.

★ Home assistant - do you like the concept of what "Siri/Alexa/"hey Google!" can do, but don't want the surveillance devices in your home? They make open source versions that work similarly (but with less surveillance) than the "big boy" brands.

★ Home security system - (think "Ring" et al). Run it yourself so nobody at Security Company HQ can watch you in your sleep, right?

★ Open source home controls ("home automation") - the main computer that can control all your "smart" air conditioning systems, lighting systems, laundry systems, dishwashers, refrigerators and all that shit. Why pay a third party to surveil you?

To get started, I recommend this site: https://docs.mrchromebox.tech/docs/getting-started.html which goes over what you need to know about choosing the Chromebook that will work for this project.
I also recommend this page: https://docs.chrultrabook.com/docs/firmware/supported-devices.html#supported-platforms which is about as up to date as one can get on which Chromebooks are usable as linux machines. For instance, Chromebooks running cell phone CPUs won't run linux.

If you go Googling, you will be assured that linux runs on any Chromebook, and wonder why I'm making such a big deal out of this.

Google will happily allow you to run linux software on top of ChromeOS. It'll work just fine, too.
Except that Google will know everything you do on the device and can change how the OS works whenever it wants.
For your own privacy and security, running linux directly on the "bare metal" of the Chromebook hardware is the recommended method here.

I prefer surplus Chromebooks because they're an "all in one" unit (they come with display & interface device [touchpad]) so you don't need to buy an extra keyboard, monitor and mouse (but if you've got those things laying about, there are surplus Chromeboxes out there).
Ubuntu comes with a software package called "gnome-tweaks" which has a setting that allows the screen only to sleep when the display is closed (allowing the rest of the machine to stay running so it can be accessed 24/7).
The linux running on the Chromebook can also be accessed over the network (no need to drag it out from behind the TV to fiddle with it [most of the time])

Chromebooks come in a variety of configurations, and it's up to you (and your pocketbook) as to what you obtain.
Do you want one with an upgradeable hard drive & ram? Older Chromebooks come this way, but the more modern Chromebooks all seem to come with integral RAM & storage (so when one of those parts takes a shit, the whole Chromebook has to be shitcanned) so when looking at these more modern options, consider how much "disposability" is worth to you.