How do religious holidays actually work in France?

In France, religious leave isn't automatically granted by law - contrary to what people often think. You have to negotiate it with your employer or take it as regular time off from your annual quota. Some big companies have agreements for important days (Eid, Christmas, Easter, etc.), but it's far from being standard and it really depends on your industry and your company. If you work in a small organization, it's usually up to you to discuss directly with your manager to work out an arrangement.

The real key is that your employer can't force you to work if it goes directly against your religious beliefs - that's protected by labor law, but you really need to document why it's a problem for you. What people often forget when reading general explanations is that it's not an automatic right like "I have a religious holiday so boom paid time off" - your boss can totally refuse if it creates a real organizational issue, unless it's actually a reasonable and accommodating request. The best strategy in practice is to ask well before your important date, propose solutions (working from home, swapping days with a colleague, making up the time later) rather than just "I'm not coming in," and keep a written record of your requests.