It isn't the English r, and it isn't a gargle either. A gentler way to find the sound at the back of your throat.
The French r is the sound learners stress about most, and the advice to
“just gargle” rarely helps.
Where it lives
The sound is made at the back of the tongue, near where you’d say a soft g
in “go”. Try saying “aga aga aga” and then let the back of the tongue relax
into a light friction. That friction is your r.
Don’t overdo it
A heavy, scraping r sounds like a caricature. In everyday speech it’s
surprisingly soft — often barely there at the end of a word like quatre.