Almost all ways to sync Obsidian has a problem with multiple people editing the same file.

Although there are some tools for better collaboration, but if it's just for one particular file it might be a bit "overkill".

But to give them a mention: Relay and Screen Garden are two community plugins that do it, HedgeDoc is a different app but it is a collaborative markdown editor, then the core team of Obsidian is also working on the multiplayer update.

Sure, lots of apps have this issue but I assumed it would work since they advertise the feature: https://obsidian.md/help/sync/collaborate