The .zip-file that contains the offline version of kn Secrets can be downloaded here.
To verify that the .zip-file is genuine, use any appropriate tool to compute its SHA256 hash value. The SHA256 hash value should come out to be
6f746d69dca5f31aca75e01b8951a9e7aa92bc6fd98e99f98bbe4262eda28d75.
Once successfully verified, unzip the file into a directory on your disk, find the file "index.html" in that directory, and double-click that file to start kn Secrets in offline mode. Please follow the security guidelines whenever using kn Secrets in offline mode.