You need Linux to run CHIRP on a Chromebook. IMNSHO, however, the best Linux solution for a Chromebook is NOT Google's Crostini (the "official" way), which has been and still is a "work in progress." (Others may disagree, and that is fine, and
it is totally your choice). The best solution by me is Crouton, developed by a Google engineer, Dan Schneider. Crostini only allows you to run Linux apps, it does not provide a full LInux desktop, and requires you to do most everything from the command line.
Crouton provides a full Linux desktop (I prefer xfce) so you have a nice graphical interface much more like what you are used to. Also, there are a number of Chromebooks, including my high-end-for-2017 Asus Flip c302 for which for whatever reason Google did
not even make Crostini available (oddly, it works on a lot of older and less powerful Chromebooks).
Here is a very complete article on installing Ubuntu with Crouton.
Here is an article that is also required reading, since some of the steps have changed due to changes in ChromeOS. I also explains how to use different versions of Ubuntu, and do a lot of other cool stuff. Be
sure to install the Crouton extension in Chrome, it is necessary to share the Clipboard between Chrome and LInux. This is all explained in this article.
Now, don't be afraid of putting your Chromebook in Developer Mode. It is "not secure" but it is still more secure than a Windows or Mac computer. The main vulnerability is that somebody with PHYSICAL ACCESS to your Chromebook could do bad things. It does
not expose your Chromebook to bad things from the Internet.
So after you have Ubuntu installed, you need to install CHIRP. Installing and running CHIRP requires three commands on the command line. It is explained
here. One cool thing about CHIRP under Linux is that updates are made with a single command at the command line. The command line can be intimidating, but for the most part you
can copy and paste from the web pages into the Linux command line terminal.
I probably left something out, but give it a try!
Pat Anderson
KD7OAC