This British speaker uses "whom" sometimes, but generally only after a preposition. I wouldn't use it the way it's used in this lesson, but it's not wrong, of course. This is not because I lack "a deeper knowledge of grammar", but because I understand how it is actually used in modern English, and I wouldn't want to sound pompous. I am afraid that non-native speakers who think that they are following the "rules of grammar" will just end up sounding like non-native speakers.

Agree with all that's been said. Maybe one can take some of the lesser used grammatical distinctions, those that have been blurred and lost over time, as an opportunity to brush up on the finer points of English grammar. "Who" and "whom" distinguishes between direct and indirect object in English. When you understand which to use when, you'll have an easier time learning the French distinction between those two concepts.

en Angleterre aussi

As a rather ancient Brit, I’d agree that "whom" as a direct object sounds stuffy and unnecessarily formal. But I did take exception to the bit in your article that says "Here in the UK, in contemporary English, no one would ever use the syntax "He ate only sweets"!! This seems still to make a useful distinction (and reminds me of John Lennon in Imagine:  "above us only sky", though I guess that’s hardly contemporary English now)

Agree with this completely, I'm English born - 29 now, and when I came across the 'Qui est-ce qui'/ 'qui est-ce que' lessons, my first thought was 'I have no idea how to use 'whom' in English'. Whilst I understand this is a french learning site, I do think a very brief refresher on whom may be useful to help with the distinction. Especially as I didn't know what a indirect pronoun was until I started learning french