Messages windows won't open from tray

Mail
#1

Hi,
after installation eM client nevertheless v.8 or v.9 I can open/reply one or two mails. After that all reply windows appear and sit in tray, no way to open it!
What I’m doing wrong?
Windows 10 Pro (20H2)

#2

The window may be off screen.

Hover your mouse over the taskbar icon. When the thumbnail appears, right-click in the thumbnail and choose Move. Use the keyboard arrow keys to bring it back on-screen.