Yes, using unauthorized signal boosters in France may lead to penalties[1]. The National Frequencies Agency (ANFR) regulates signal boosters, and certification from ANFR is mandatory[1]. Using uncertified signal boosters can result in penalties[1]. However, according to the Autorité de Régulation des Communications Électroniques et des Postes (ARCEP) regulations, it is legal to use mobile phone signal boosters for homes and businesses in France, and no license is required for boosters that boost signals for any cellular network in France[5].
Citations:
[1] https://www.mobilesignalguru.com/blog/legal-requirements-and-regulations-for-mobile-signal-boosters/
[2] https://www.federalregister.gov/documents/2013/04/11/2013-07396/signal-booster-rules
[3] https://nextivityinc.com/blog/mcmc-fines-up-to-rm500000-for-using-unauthorised-mobile-signal-boosters-and-repeaters/
[4] https://www.weboost.com/blog/regulation-myths-about-cell-signal-boosters
[5] https://mysignalboosters.com/fr/faqs/
[6] https://transition.fcc.gov/oet/spectrum/table/fcctable.pdf
[7] https://mysignalboosters.com/fr/terms-and-conditions/
[8] https://www.law.cornell.edu/cfr/text/47/20.21