@ops159 thanks for your reply.
I’m not quite understanding the issue and configuration you have in the AMP plugin clearly.
twenty nineteen themes not running. but the old version ran an amp theme. but the customizer mode was not turned on..
Both the main customizer and the AMP customizer should be available at all times when using Reader Mode. If that is not the case then we’ll need to investigate a potential conflict.
Do you see any errors in the PHP error logs or using the WP DEGUG log in your environment?
Also, feel free to send a screenshot or short video of your experience which may help.
You can provide a link to screenshots using a service like Imgur or Jumpshare. Or record a short video using Recordit.