Warning when opening wxPython GUI

To find the cause, it’s a good idea to start with the simplest program, excluding all dependent packages, and see if the problem occurs.
Btw, did you already try @Robin’s prescription?
see: “wxPython4.1.1 Python3.8 locale wxAssertionError - #3 by Robin

import locale
import wx

def check_locale():
    print(locale.getdefaultlocale()) # ('ja_JP', 'cp932')
    print(locale.getlocale())        # (None, None)
    wxloc = wx.GetLocale()           # None
    if wxloc:
        print((wxloc.Locale, wxloc.Name))

class App(wx.App):
    def InitLocale(self):
        import sys
        if sys.platform.startswith('win') and sys.version_info > (3,8):
            import locale
            locale.setlocale(locale.LC_ALL, 'C')
    
    def OnInit(self):
        wx.Log.EnableLogging(False)
        frm = wx.Frame(None)
        frm.Show()
        wx.CallAfter(check_locale)
        return True

app = App()
app.MainLoop()

:memo: InitLocale is called before OnInit.