KopiaUI does not load after upgrading from v0.18.2 to v0.22.3

I have been running kopia v0.18.2 as a server on a Mac under macOS Big Sur (macOS 11.7.11) for two years. I also used kopiaUI on this server to get access to the repositories.
I upgraded kopiaUI today but now, kopiaUI does not load anymore. Whatever I choose in the menu (Starting up, Connect to another repository, …), I get a blank window with “KopiaUI is loading”.

When I quit kopiaUI, I get an error message “A Java script error occurred during the process.
Uncaught Exception:
TypeError: Cannot read properties of undefined (reading ‘loadURL’)
at Timeout._onTimeout (file:///Applications/%E3%83%BBApplications%20non%20Apple/KopiaUI.app/Contents/Resources/app.asar/public/electron.js:145:41)
at listOnTimeout (node:internal/timers:588:17)
at process.processTimers (node:internal/timers:523:7)”

Nevertheless, the kopia server can be accessed by clients.
What can I do to solve my problem?