thank you for your reports, I checked it with the QA and Dev, they are aware of this issue.
Once the upgrade fails, can you please collect the logs as described at https://support.eset.com/en/kb3404-use-eset-logcollector-on-macos-and-send-the-logs-to-eset-technical-support?ref=esf
upload them to a safe location and send me a private message with the download details and reference to this forum topic?
Once you do, the work-around is to disable the Web access protection to apply the upgrade.
Yes, I can confirm this behavior on at least macOS Big Sur devices. I opened a ticket with support and was essentially told that ESET support for Big Sur is not fully available even though their public facing support page says it is fully supported minus the firewall and device control. I was told full support is coming in March with a new version that I hope fixes this. It is rather annoying to have to uninstall ESET to install critical OS patches.