Syncovery is now in the QNAP AppCenter. However, sometimes the version on this page can be a bit more recent.

QNAP packages v9.39 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