Have you considered a distributed filesystem such as GlusterFS or DRBD? I believe those support synchronous replication so writes will go to all the configured machines before acknowledging the write. Performance will likely take a hit the greater the number of clusters in the cluster.

Remember wifi can be an issue, even if you don’t have anything exposed outside. If you have a router that comes with a weak password ensure you have changed it.

Obsidian with paid sync feature. Have obsidian on multiple computers and devices and don’t have to deal with setup or management of the sync process.