That I have files with enormous thousands of components and Figma doesn't miss a beat. If you're able to get vector versions of those, then the speed shouldn't be an issue. Obviously if there are a lot of photos, that might be tough.
Having been a long-time user of Figma's somewhat-trailing (at this point) competitor, Sketch, speed is surprisingly one of Figma's most immediately-apparent advantages despite being web-based rather than MacOS-native.
At a previous job, we had a Sketch file that contained more or less an entire B2B app, and at hundreds of megabytes, it took tens of seconds to load (not asynchronously, either, blocking the UI until the whole thing was in memory). A similar everything-file at a more recent job where we used Figma was like night and day: something like three seconds until the file was usable, and perhaps a few more seconds for any big images to load.
Then there's Figma's upstart competitor, Penpot. In my initial explorations, it felt about as responsive as Figma, but when I loaded one of their tutorial files – not even a mega-B2B-app file – everything slowed considerably. The load time wasn't bad, but the frame rate for simply scrolling around the artboards dropped like a rock. While I'm bullish on Penpot, they have a long optimization road ahead of them.
In my experience they dive in and don't think about it, it's just natural to use. Not to say the UX is ideal, because imho it sucks hard, but no one complains about *having to use a webapp when they open figma.