Which meetings? Some are more closed door than others. The big committee meetings are open door, anyone can come (pre covid). There are official ISO votes where you need to have your countries' blessing to vote (one vote per country), but most votes are just straw polls and anyone who shows up can vote.

There are also core teams that are closed door. And sub committees, some of which are more welcoming of outsiders than others. In the end though, if you submit a paper the relevant committee will read it and then invite you to come talk about it (at your expense to get there, but they will find a sponsor if needed).