The term "microkernel" here is key. The Btrieve engine runs as a thin layer between your application and the OS file system.
Classic Btrieve 6.15 is 32-bit, 4GB file limit, no Unicode. Upgrading to Actian Zen 16: The term "microkernel" here is key
If you are running backups, use the Continuous Operations mode to prevent file locks while the backup software runs. Performance Tuning 4GB file limit