[WxPython] Linux: No module named 'wx'

[PeterLinux]

When I run my little Python script in the shell, I get the following error:

Error:
Traceback (most recent call last):
  File "./learn.py", line 6, in <module>
    import wx
ModuleNotFoundError: No module named 'wx'

I use:
Xubuntu Linux 18.04
Python 3.8.2

In /usr/lib/wx/python/
are these files:

Output:
wx3.0.pth
wx.pth (a link to /etc/alternatives/wx.pth)

I already tried building Python from source (successfully/without errors) and installing with apt wx3.0-headers and wx-common. How can I get "import wx" working?

Thanks in advance for any hint, greetings
Peter

---

I've boiled down the script to this:

#!/usr/bin/python3

import wx

(Now the error occurs in line 3, not 6.)