The claim slightly understates Russia's population: the official Rosstat estimate is ~146 million (1 Jan 2025), i.e. ~6 million / ~4% higher than the 140 million stated.
Rosstat's headline figure includes Crimea (annexed in 2014) and other occupied Ukrainian territories; excluding them the population is about 144 million (BOFIT), still above the claimed 140 million.
The figure is presented rhetorically ('only 140 million') to magnify the demographic contrast with the EU; the underlying order of magnitude is nevertheless essentially correct.
SecondaryTASS (citing Rosstat)"As of January 1, 2025, the preliminary estimate of the population of the Russian Federation totaled 146,028,325 people. The population dropped by 0.08% in 2024"