By 'major' I mean organizations that have more than half of the total number of UN states participating and/or all five of the permanent members.
By intergovernmental organization, I mean any body that has a budget, regular staff, and official recognition by the above number of countries whether via ratification, signatories, memorandums, etc. Ideally for it to count all participating countries must pay dues to it in some form. Though this information may be too hard to source.
To count as separate organizations there should be some degree of autonomy.
Some of my research:
There's this list on wikipedia: https://en.wikipedia.org/wiki/List_of_intergovernmental_organizations
But it includes many organizations only of a regional nature.
There's also the Yearbook of International Organizations: https://uia.org/yearbook/
But they include many NGOs as well.
The minimum number is the total number of organizations associated with the UN system: https://en.wikipedia.org/wiki/United_Nations_System
Which gives 60+ organizations, depending on how they're counted. Yet organizations like the WTO exist outside the UN system and are also clearly major intergovernmental organizations.
In other words, how many such organizations are there beyond the UN system?
