Syncovery is now in the QNAP AppCenter. However, the version on this page is usually more recent.

QNAP packages v10.11.11 for installation with AppCenter:
 
QNAP Intel/AMD 64-Bit Package  QNAP Intel 32-Bit Package
 
QNAP ARM 64-Bit Package 
 

For QNAPs with 32-bit ARM processors, there are three different packages. The left-most one is for the newest CPUs. Which one you need is best determined thru trial and error. The App Center will tell you if it can install the package or not.

ARM-x41  ARM-x31  ARM-x19