Alfred Wegener spent the last two decades of his life being professionally ridiculed for an idea that turned out to be correct.
What actually happened
Wegener proposed continental drift in 1912, the idea that the continents had once been joined and slowly moved apart. The geological establishment of his time dismissed it outright, one contemporary derisively diagnosed him with "moving crust disease." By 1930, the year he died on an expedition in Greenland, his theory had been rejected by most of the field and had sunk into obscurity. It was not until the 1960s, thirty years after his death, that the discovery of seafloor spreading and the development of plate tectonics proved him right. Geologists today accept the basics of what he proposed as fact.
Why the current verdict is not the final one
Being dismissed, mocked, or overruled in the room right now is a snapshot of the current consensus, not a verdict on whether you were correct. The reverse is just as true, and it is the sharper edge of the actual saying, whoever is currently winning, currently right, currently being agreed with, is not guaranteed to still be the one holding that position once more evidence arrives. The laugh that matters is the one that is still standing at the end, not the one happening loudest right now.
Where to start
If you are confident in a well-reasoned position that is currently being dismissed, the fact of the dismissal is not itself evidence you are wrong, it is evidence about the room's current state of belief, which is a different thing entirely.
Keep the reasoning documented and keep looking for the evidence that would actually settle it either way. And when you are the one currently winning an argument, hold it a little more loosely than it feels like you should, reversals happen to the confident as often as to the doubted.
Reading whether a currently unpopular position is actually well-reasoned, versus just uncomfortable to let go of, is a judgment worth being honest with yourself about before you decide to hold your ground. What this gives you is the reason the room's current verdict is not, on its own, the evidence either way.
There is a specific way to hold a currently unpopular position without it reading as stubbornness, documented reasoning, openly stated, rather than repeated insistence, and it is worth having ready before your next real disagreement.