The Synod was consultative by design, and for fifty years the pattern held: the assembly discussed and voted on propositions, and the pope wrote the document. Francis changed the instrument twice. The apostolic constitution Episcopalis Communio, issued in 2018, provided that the final document of an assembly, if the pope approves and orders its publication, participates in his ordinary magisterium, which gives an assembly text a standing it did not previously have. The same constitution formalised a consultation phase reaching into dioceses before an assembly meets.
The synod on synodality, running from 2021 through assemblies in 2023 and 2024, applied that at full stretch, with parish and diocesan listening stages, national syntheses and continental assemblies feeding the working document. At the 2023 assembly, for the first time, a number of members who were not bishops, including women, were voting participants alongside the bishops. The change was made by the pope's decision and was reported and argued about worldwide, and it is the sharpest single illustration of what the instrument now is.
None of this makes it a parliament. The pope convokes it, sets its topic, appoints a share of its members and decides what follows from it. It is also not the same institution as the standing holy synods of the Eastern churches, which govern their churches rather than advising a bishop of Rome.