However, to pinpoint the specific syntax error rather than a generic "incompatible" message, one must increase verbosity:
If you are seeing this on a system that was recently updated (or is in the middle of one), ensure all updates are either fully applied or cleared. Clear Staged Updates (macOS/OCLP) : Use tools like the PurgePendingUpdate tool or manually remove files in pf configuration incompatible with pf program version
Reload rules: