Individual civilian afghans are not embargoed by US law - it's not Iran. The Taliban are, of course, embargoed and listed in various things like the OFAC list.
Hundreds of thousands of ordinary Afghans have gmail accounts, many companies use google workspace or office365, etc. For example.
I think the point was that having an Afghani publish the source wouldn't really accomplish anything because Facebook could just go after whatever service was used to publish it, instead of the person who published it.
An Afghani can access GitHub or the chrome extension store, but those are both run by American companies who will obey Facebook's takedown requests.
At least that shifts the dangerous legal-financial burden onto google's lawyers, if they want to fight a takedown request to remove an extension from the extension store.
A takedown request is only binding on a well-capitalized firm like Google if it is based on some legal rationale that could survive a test in court. It isn't clear that the request under discussion has such a rationale. At the very least Google would take this to some court and force a judge to say something about it.
Once a firm grows accustomed to following orders from their competitors, bad times lie ahead.
YouTube obeys DMCA with respect to copyrighted media. DMCA is an established system that allows services like YouTube to exist in the first place. The threat letter doesn't mention DMCA or copyright, because this extension couldn't possibly be perceived as infringing on copyright. Instead it speculates about trademarks and TOS violations. There isn't a standardized takedown regime related to those. TOS is not law.
It's true that some low-level manager in the chrome web store organization might just submit to this sort of letter. It would be a mistake for such a manager to ever receive this sort of letter. This is for the legal department. There's no way that a competent general counsel would decide that the best strategic move is to just follow the orders of major competitors. Google already employs dozens of lawyers; it's not costly to send a couple to court. In this case, the PR alone would be a huge win.
if you really want to make a DMCA complaint against youtube they will honour it, but they try to push all requests through their own DMCA-alike system that lets copyright holders file takedown notices, but it doesn't have any legal standing under the DMCA or any other country's copyright laws. the youtube takedown notice system is basically "if you ask nicely we'll take it down".
Sure, the YouTube (not Chrome Web Store which is a completely different organization) system requires far more of creators and far less of "owners" than DMCA specifies with respect to copyright. We're still talking about copyright. The extension under discussion cannot be construed as violating copyright, or even facilitating violation of copyright. That's why even the crazy overblown threat letter doesn't mention copyright. It probably would have, even if it did so without justification, if the end goal had been to take down a YouTube video. The end goal in this case was actually to take down a Chrome extension, which is only similar in the sense that the people who make such a decision also work for Alphabet.
Now you're into territory where yes, the extension is available, but nobody can find it and only the very technically astute will be able and willing to install it. FB achieves 99.9% of their goal.
Hundreds of thousands of ordinary Afghans have gmail accounts, many companies use google workspace or office365, etc. For example.