How are you applying the custom styles or a ‘feature’ of Astra?
If it is custom code are you using
I don’t know how to use custom code. I used Astra’s theme builder to specify the background color and font color.
Reference image: https://i.imgur.com/AdRWSsq.png
Can I change the background color to black in the Block Editor, or rather change the font color to black?
OK if you have no custom code them the issue is Astra Theme Builder compatability with 5.7 and so you should raise support with Astra.
The free support is here https://wordpress.org/support/theme/astra/
Is Astra Theme Builder a paid for product?
Yes, I am using Astra pro.
Thank you for your kind response.
I should ask the Astra team.