I had to downgrade spyder too, using:
sudo downgrade spyder
sudo downgrade python-spyder-kernels
(the first from 5.0.0 to 4.2.5 and the second from 2.0.1 to 1.10.2)
Otherwise, got the error message:
No QCoreApplication instance found. Application patches not applied. You have to call load_stylesheet function after instantiation of QApplication to take effect.
Traceback (most recent call last):
File "/usr/lib/python3.9/site-packages/spyder/app/mainwindow.py", line 2146, in create_window
main.setup()
File "/usr/lib/python3.9/site-packages/spyder/app/mainwindow.py", line 810, in setup
CONF.set('help', 'css_path', css_path)
UnboundLocalError: local variable 'css_path' referenced before assignment
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/bin/spyder", line 33, in <module>
sys.exit(load_entry_point('spyder==5.0.0', 'gui_scripts', 'spyder')())
File "/usr/lib/python3.9/site-packages/spyder/app/start.py", line 213, in main
mainwindow.main(options, args)
File "/usr/lib/python3.9/site-packages/spyder/app/mainwindow.py", line 2293, in main
mainwindow = create_window(app, splash, options, args)
File "/usr/lib/python3.9/site-packages/spyder/app/mainwindow.py", line 2148, in create_window
if main.console is not None:
File "/usr/lib/python3.9/site-packages/spyder/app/mainwindow.py", line 1159, in __getattr__
return self.get_plugin(self._INTERNAL_PLUGINS_MAPPING[attr])
File "/usr/lib/python3.9/site-packages/spyder/app/mainwindow.py", line 168, in get_plugin
raise SpyderAPIError('Plugin "{}" not found!'.format(plugin_name))
spyder.api.exceptions.SpyderAPIError: Plugin "internal_console" not found!