Does Time Capsule MC344J/A work with MacOS High Sierra?

You can use the Time Capsule (TC) as a file server. However, it was designed to be used for Time Machine (TM) backups.

Regardless of which you use it for, the following would be important to know:

• Use the TC either for TM OR as a file server, not both simultaneously.
• As a file server, the TC can share out its drive to either Macs or PCs. However, PCs rely on using the SMB file sharing protocol to access the TC's file server. In addition, the TC's file server only supports SMB v1.0. This is a very outdated version and lacks any type of useful security.
• You can connect an external USB drive to the TC's USB port. You can then use this drive for either TM or for file sharing. In this case, you could use the TC for both TM and file sharing simultaneously.
• Data transfer speeds to both the internal TC driver or to an attached drive are not stellar. Just be aware that copying large files may take some time.