According to the documentation setting this to 0 disables it.
KEYLOGGER_BLOCKING_ENABLED
Determines whether keylogger blocking is enabled. A value of 1 enables the feature. A value of 0 disables the feature. The feature is disabled by default.
https://docs.omnissa.com/bundle/HorizonClient-WindowsGuideV2406/page/InstallHorizonClientFromtheCommandLine.html
I have found less filtering is better in the interop matrix. I just used Horizon and Horizon Clients.
https://interopmatrix.omnissa.com/Interoperability?col=23,&row=108,
8.3 is almost 3 years old. Is there a reason that you are using this old of a version. 8.12.1 is available for client versions. What version of Connection server/agent is in use?
I have seen this happen when a client does not have the required protocol available. In these case Horizon can allow for the other.