A friend gave my kid an unused Chromebook last week. I believe it’s an Acer R11. The first thing I saw when starting it up was that security updates expire in June, 2022.
I’m not going to worry about it for our planned usage. My kid will use it to watch shows, play games, and maybe do some very light web browsing. The worst that happens if it’s hacked is that maybe somebody steals my Netflix login credentials.
Now, if it was going to be used for more security sensitive stuff, then I would be much more concerned. It will probably work normally for a long time, and you won’t notice any changes.
At some point some vulnerability in Chrome (the browser) will be found, and if it’s really bad, then some ad on a webpage could install nasty things. You likely won’t have any warning that is a problem. Just one day (worst case scenario) every password you type is sent off to somebody else.
If you ever do things on it like login to your email or check your bank account, then plan on retiring it in the next few months.
You can try installing Linux on it if you want, but at this point it’s probably old and slow enough that it’s worth spending a few hundred on a new one, if you can afford it. The new one should be faster and better.
So, TL;DR: It will keep working just as well on July 1 as it works today. But, at that point it is a ticking clock until some security vulnerability makes it too dangerous to use. That clock could run out in days, or never, but you have no way of knowing. Plan to replace it this summer, if you can afford to.
That’s all assuming you decide to keep it on ChromeOS, if you switch to Linux, then it should be fine as long as whatever you install is supported.