The indifference they mean is not equilibrium but the real power of acting and not acting
When the teachers of the Roman Church speak of the indifference that either makes up the essence of freedom or at least necessarily goes with it, they do not mean a state in which the will wavers between two opposites, leaning no more to one than to the other, hanging as if in balance and pushed this way and that by the slightest weight.
They grant that freedom is present in someone who is not at all indifferent in that sense. His will may be strongly inclined to certain actions by deeply rooted habits, and he may have a settled purpose of acting this way and no other, from which he can be moved only with great difficulty.
The indifference in which, in their view, freedom of choice lies is nothing else than a real power of acting and not acting. It remains even in someone whose mind and will are fixed on acting by a firm and steady purpose.
Latin
XLIII. Porro Doctores Ecclesiae Romanae per indifferentiam illam quae libertatis essentiam, vel constituit, vel saltem necessario sequitur, significare nolunt eum voluntatis statum in quo inter duo opposita nutat, neque ad unum magis inclinat quam ad alterum; sed in aequilibrio quodammodo suspensa, paulo momento huc & illuc impellitur. Agnoscunt enim libertatem in eo reperiri qui ad agendum eo sensu minime est indifferens; sed cujus voluntas alte impressis habitibus ad certas actiones vehementer inclinata est, quique firmum propositum habet sic & non aliter agendi, a quo non nisi aegre admodum dimoveri potest. Sed indifferentia illa in qua, ex eorum mente, sita est arbitrii libertas, non aliud est quam vera potestas agendi & non agendi, quae manet etiam in eo qui fixo & constanti mentis, & voluntatis proposito ad agendum determinatus est.