On the one hand, the transition to fibre may require wiring work inside your home. There will be no direct costs for the migration, but installation costs (vertical cabling and/or other) may arise.
In addition, this migration may result in a change to your subscription, including tariffs.
If you are subscribed to an offer based on a copper connection, your operator will contact you to propose alternative offers in optical fibre or other technology.
You can also contact another operator of your choice to compare offers.