I don't think my case is exactly the same as similar earlier posted?
I bought Malwarebytes for three Macs, all running High Sierra 10.3.4. Two (one iMac at home, one MacBook Air) installed fully without problem. But the third at the office, also an iMac (2012) stalled on "Real-Time Protection is disabled". Opening System Extensions and clicking the "Allow" button for the Malwarebytes "blocked on installing" message had no effect, the button turns blue, but nothing happens, and MWB persists thad RealTime Protections is disabled. It scans manually, though. - Rebooting had no effect, nor upgrading to 10.3.5.
Note that this is a regular desktop iMac, no remote client or similar (attaching another mouse no effect). I have no idea why this office iMac is different from the one at home, it has the same system version and as far as I know the same software installed. Any idea about what could be blocking the installation?