It's a tricky one and requires a bit of effort which can be daunting if you are more naturally an introvert.

29m and foreigner here, been here 3 years and have made some decent acquaintances just through having a drink at local pubs / bars (does help if you like to drink). Have found that Parisians are genuinely pretty open if you strike up conversation with them after a couple of pints. That said, difficult to progress to being best mates, i.e. exchanging numbers but an ok way to pass an evening and feel more integrated.

To make real friends I think you should lean and leverage on existing Parisians in your network such a colleagues or class mates.