Here's a 2019 Figma article on this, not sure if its representative of their current system

> OTs power most collaborative text-based apps such as Google Docs. They’re the most well-known technique but in researching them, we quickly realized they were overkill for what we wanted to achieve ...

> Figma's tech is instead inspired by something called CRDTs, which stands for conflict-free replicated data types. ... Figma isn't using true CRDTs though. CRDTs are designed for decentralized systems where there is no single central authority to decide what the final state should be

https://www.figma.com/blog/how-figmas-multiplayer-technology...