I’d recommend storing the “authoritative” version of your project files on a NAS, and then sync’ing them to your local machines when you want to work on them. For best performance, they need to be on your local SSD (not a USB attached one) to minimize latency and maximize throughput. Then sync them back to the NAS, and sync them to that other local machine to work on the project elsewhere. Make sure your directory structures are exactly the same on both of your Cubase machines, and you shouldn’t have problems with missing files etc.
This is the setup I’m using personally: The authoritative copies of all my Cubase files are stored on a Synology DS220j NAS connected via (wired) GigEthernet to multiple machines. I use GoodSync to sync these project files to and from my local machines, which have NVMe SSDs built in. This setup has been rock-solid and reliable for years, and you get the added bonus of having your precious Cubase project files stored redundantly on the RAID array in the NAS. For extra protection, I’m also sync’ing those files to the cloud, so even if my house (and all the gear) burns down, I’ll still have my Cubase files 