For specific STQC-supported firmware versions (often required for government or secure installations), specialized lists are sometimes maintained on Infosec Solutions .
The most reliable source is the official CP Plus Support & Download Center. You can search by the model name CP-UNR-4K2161-V2 . cpunr4k2161v2 firmware download link
Official downloads and technical support are available directly through the CP Plus World Support Portal Official Product Page: cpunr4k2161v2 firmware download link