Broadcom has essentially disabled access for anyone to download any version of their desktop hypervisor products released prior to the November 2024 announcement that they are "free for personal, educational, and commercial uses". Yes, even if you have a valid license for an older version, you can't download the installer. Those that have a support contract are a little better off - they supposedly can download older versions until their contract expires. The "gotcha" here is that they are no longer selling support contracts, so soon even contract customers will be in the same boat.
The issue you're seeing with the in-product updater is that these older versions have not been changed to reflect Broadcom's changes in their product delivery infrastructure. And VMware Fusion 11.5 has been end-of-support for quite some time now, so they're not going to go back and fix it.
There is a back-door method to get old updaters though (they are not "full releases",) You'll have to unpack them and move the VMware Fusion.app file contained within it to /Applications yourself.
First shut down all your VMs (don't suspend them). Then exit the Fusion application.
Use this link to download the 11.5.7 updater: https://softwareupdate.vmware.com/cds/vmw-desktop/fusion/11.5.7/17130923/core/com.vmware.fusion.zip.tar
That will download a file com.vmware.fusion.zip.tar. Find the file in the Finder, and double click to open it. It will extract a folder called com.vmware.fusion.zip
In that folder you will find a file also named com.vmware.fusion.zip. Double click on that file to extract it. A folder named com.vmware.fusion will appear
Open that folder, and you will see a folder named "Payload". Open the Payload folder, and you will find a VMware Fusion application.
Move that file to the /Applications folder, replacing your existing VMware Fusion 11.5.5 application.
Now open Fusion. Provide administrator credentials if prompted.