It is recommended as standard practice for 2+ decades that users should not be admins on the workstations they use. Thus, they cannot install or update the ILLiad client themselves.

Throughout the IT industry, the way to install any software or updates is via centralized management (whether Windows or Mac workstations, or Chromebooks, tablets or phones) and automated deployments. This primarily occurs when a control server instructs workstations to install software using the workstation's own, built-in "SYSTEM" account which is a "super-admin".

The ILLiad client installer is the only software I've ever experienced (of many hundreds of applications) that fails to install when run by the SYSTEM account. Thus, the ILLIad client forces a desktop technician to visit every workstation to run the installer/upgrade as an administrator every time we want/need to update the client. That isn't really a problem when the client is on one computer, but when you have a couple dozen or more spread out over multiple, geographically distributed libraries, it is horribly inefficient and terribly frustrating.

I want to be very clear: The solution is NOT to make installation per-user. Per-user installs do mean that the user does not need to be an administrator as the software is installed within the user profile. However, per-user installs are universally despised among sysadmins because they are a PITA for managing centrally.