Should be fixed now, see: https://forum.avast.com/index.php?topic=226394.msg1500785#msg1500785
Hi, the quick scan is located in custom scans.
Thank you. I found it
You’re welcome.
Version 19.3.2369 (build 19.3.4241.445)
I usually don’t focus on your program structure, but it caught my eye in the Avast Software Updater that your references to the programs I use on my system are now calling them “apps”. This is ridiculous. I update installed programs, not “apps”.
I don’t know why you have decided to forsake normal computing program terminology for the ‘kidsy’ / trendy word “apps” that Microsoft seized on also with their W10 offerings. This seems to me to go back to cell phone program terminology and has no place in standard home computer system software components.
Please change your software updater terminology and remove the useless word “apps” and correctly refer to my installed software again as ‘Programs’.
Agreed. 
Apps belong on smart devices. Programs belong on computers.
Updating Avast on our computer should definitely be a Program update.
Yes this could be a long discussion here 
we just follow here latest terminology of Microsoft. And they use now “Apps and Features”
Guess, everyone knows what an app is nowadays, so no big issue. As long as you don’t name it cupcake or such…
Hello MartinZ,
The “White UI” issue when opening Avast is not fixed for me, and it was supposed to be fixed in version 19.3.
I’m running the latest version of Avast 19.4.2374 on Windows 8.1 (64-bit), with UI version 1.0.360.
Please see the screenshot I attached.
But, they still also have:
https://screencast-o-matic.com/screenshots/u/Lh/1555076753398-94128.png