I will travel to Porquerolles on Côte d'Azur in France. I struggle about swimwear: I use to wear speedo-style swimwear and I don't really like shorts. However, I haven't been to a beach for ages, so I have no idea whether the shorts fashion hit the seas completely and people in speedos receive weird looks or not. So: Is it common for guys to wear brief-cuts at a French beach?
I think that is very subjective as it is up to everyone to choose their style.
Living on the Côte d'Azur, when I go to the beach, usually it is the older people that wear speedo-style swimwear, most of the young people wear shorts. The population is mixed so there are several people wearing speedo-style swimwear.
But honestly, I don't think people care and I haven't seen people weirdly looking at others. In fact, beaches being crowded, you mostly care about yourself getting space.
So to conclude, wear what you feel comfortable with. Most likely nobody will look at you and make you uncomfortable.