Up at the top, click/tap settings, dark mode option is in drop down.

Since you mention permissions/access denied, have you given your user permissions to use serial? You can do this with:

sudo usermod -a -G dialout $USER

What is the output of:

ls -al /dev/serial/by-id/*

What hardware are you using for hosting klipper and mainsail? Are you using a pi and mainsail os or a pi with raspberry pi os and kiauh to setup klipper and mainsail? Could you post your klippy.log?

Original dev stepped down and transferred the app to the remaining devs. See his post from5 hours ago.