According to https://shieldgeo.com/terminating-an-employee-in-france-a-gu... it would rather be roughly 1 week pay per year of seniority.

However it is hardly comparable as unemployment benefits would kick in (on average 72% of your previous salary after taxes, maximum duration 24 months with decreasing amount). For instance if you worked 3 years and your annual salary was 80k, you could get a benefit of 57k over 12 months.