Not sure what you mean by 'night mode screen'. Did you have a 'dark' theme that was disabled after updating TB?

A black background with white printing if this is a 'dark' theme

If you were using a theme which you downloaded then it would be here: 'Menu icon 3 bars' > 'Addons' > Themes (icon is an artist palette) What theme were you using ? Maybe it has been disabled. you could try the default dark theme

However, if you are using Windows OS then you can change the general UI of computer by selecting to use 'High Contrast'.

eg: see image below computer 'Control Panel > Personalization' > Window colour and Appearance' select eg: 'High Contrast black' click on 'Apply' click on 'OK'

There are a few dark themes that work in TB 60:

TT DeepDark, Metal Lion Sea Monkey, Monterail Full Dark

https://addons.thunderbird.net/en-US/thunderbird/complete-themes/?sort=updated

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

Thank you so much - all is back to order. Was helpful to look at the ideal case as well.