Yes. The real estate capital gain corresponds to the difference between the resale price of the property and its acquisition price. To reduce this amount, it is possible to increase the acquisition price of a certain number of costs and expenses, which have been exhaustively listed in the General Tax Code, including the expenses of construction, reconstruction, enlargement or improvement carried out on the property. (art. 150 VB, II, 4° CGI). The costs incurred are considered, either for their actual amount, under certain conditions, or at a flat rate for an amount of 15% of the acquisition price, provided that the taxpayer sells the building more than five years after its acquisition. The flat rate option is of interest when the taxpayer is unable to justify the expenses that have been incurred, or even when he has not carried out any work. Indeed, in the absence of giving precisions on the General Tax Code, the administrative doctrine considers that the taxpayer does not have to establish the reality of the work (BOI-RFPI-PVI-20-10-20-20 §390).
Careful however, as the decision of Council of State would suggest that the tax authorities could request proof of this work during an inspection (CE, 3° Ch. 25 March 2019, n°422943). If this decision is isolated, it is recommended to remain cautious.