These are the instructions for how to extract the MSI installer (x64) file from the 21.2.804 version (and newer versions) client installer .exe file, that is typically used to automate the backup client installations (for silent install pushes), which works differently to any of the prior older backup client versions in that case, in that the makeup of the files in the .exe is very different. The format of the 21.2.804 version client installer .exe changed recently, between even 21.2.404 and 21.2.804 from what I can tell in brief testing, using even the standard 21.2.804.5 (non-custom build or non-Cloud/MSP client build) client .exe download file. To extract the x64 .msi file from the 21.2.804 client installer .exe (or newer version) file, open that .exe file using 7-Zip, and double-click on the first ".rsrc" folder in the list, at the top, that is seen in my screenshot below at the top right of it, then double-click on the "RES_CAB" sub-folder under the ".rsrc" folder, and then copy all of the .CAB files in that folder (there are 4 x .CAB files in my case for the standard 21.2.804 client download .exe file, but your .exe may differ there) to your Downloads folder, such as to a new "\Downloads\21.2.804.5_CAB_folder\" in my example screenshot below, and then open the first "SETUP_BACKUP_CLIENT_1.CAB" file using Win Explorer in that folder, and it should open and list 2 x .msi files, then select the x64 .msi file in the list and copy it out to the one prior folder to that, and that will get you the "BackupClient64.msi" file to execute by double-clicking it via Win Explorer to start the x64 client installer that way (which I haven't tested myself beyond that, but I can see that the client installer app does launch, and it prompts to press "Next"). The single screenshot below should help you for this:
Note: In the above instructions set, just to be clear or as a caveat to mention, do not try to double-click on the ".. CLIENT_1.CAB" file inside 7-Zip in order to run the .msi file that way, as that got an error for me when attempting it, copy the *.CAB files out first, then open the ".. CLIENT_1.CAB" file via Win Explorer, and then you can either run the x64 .msi file that way or copy the x64 .msi file out somewhere and then run it directly via Win Explorer, by double-clicking on that single x64 .msi file, to launch the NovaBACKUP x64 client installer app.