Living in France, I can tell, France is very startup hostile.
The amount of taxes a company has to pay and the amount of paperwork to do (or money to delegate it) is just absurd.
The only way a small tech company can make any money and be sustainable (let alone grow) is having all employees as associates (with all the organizational problems that such thing will bring) and take dividends instead of salaries, otherwise literally more than half of the salary is gone in taxes.
And of course, this is all having their own day job, or taking a "company creation" sabbatical year, which is the only actually helpful thing for startups you'll find in France. You can take a year off from your job, try to create a company, and after the year your employer has to take you back in the same position (if you want, obviously). You need to have worked a number of years before, both in global and with your current employer, though.
VC culture is close to non existing, so you need very good connections to have investors, and those connections often times aren't in France. Financial and investing groups in France are very conservative.
Literally all new companies I've seen founded are like that, and from those that live longer than a year, about 50% move their HQ elsewhere, normally the place where the funding came from.
With the numbers we made back in the day (we were 5), the gap from "we're making some money on the side" to "we need to hire someone who isn't a founder" was about €300,000 yearly in extra revenue. Otherwise it wasn't worth it.