Check for updates seems to work for me, but it does something different than in 4.0.0 ... The "flash" icon is always red (I'm not sure, but I think it used to be yellow when there were no updates) and when I click on it, a window comes up with three buttons:
You have the latest version.
Jdi na seznam
[Go to] [OK] [Help]
The Go to button opens a browser window with https://www.seznam.cz/
For 4.0.1 I got the multilingual installation package (previously I had the English version), I don't know if this makes a difference.