I was there and we were around 50000. It was not only against domestic violence but against all violence on women (for free abortion, against FGM, against street harassment...).
Violence against women is terrible in France. In 2019, 137 women have been killed by their husband / boyfriend /ex (and this number is still going up) 93000 women are raped or tentatively raped every year.
The government is putting forward a proposal to try to improve the situation and the idea was to try to put pressure on them.
Not sure it will have any effect, but it was nice to see all these people gathered for women. I met some lovely 'early feminist who were in the street in 1975 when abortion was made legal in France.