Post title says it all. I just had to restore from backup as there was no simple way to recover from this issue.

I filed a bug report for this issue at https://bugs.kde.org/show_bug.cgi?id=426233

Confirm here. How to change to previous versions ?

apparently, at that moment qt 5.15 files have been removed from mirrors

srgmro33 wrote:apparently, at that moment qt 5.15 files have been removed from mirrors

Probably a good thing.

I was in KDE Matrix developer room and saw this, do any of you have neon.list with release in it instead of user?

Quoted from Matrix 7/9/20 10:09 GMT:
"
totof:
upgraded has landed on my user flavour this morning
my user neon is actually broken .... sddm doesn't start as kwallet and others ... due to upgrade to partial qt version 5.15 upgrade
some packages are in 5.14.2 for qt and others are on 5.15
I use my windows with webirc for now ... due to break neon ...
and I know it's ugly or bad or whatever
sitter:
I don't see it in user repos https://archive.neon.kde.org/user/pool/ ... ource-src/
totof:
release ... sorry .. my
it changed from user to release since focal migration
sitter:
well, release is for testing and you've found it to be broken
if it randomly changed that sounds like a bug
though I don't know where that bug would be TBH, there's nothing that ever touches the neon.list after installation I think
totof:
\o/ ... I've found the problem ... need to switch it on my neon sources.list files and after need to downgrade ... and all with my laptop with RJ45 ...
thx for the info ... now need to try to restore in user ..
"

Edit: This was posted an hour or so after:
"
totof-at-work
for information : fix my issue was ... change the neon.list files by replacing release by user, then apt update then downgrade qt to 5.14.2 then apt install neon-desktop for reinstalling some missing packages as sddm
and yipi it works again
"

I was in KDE Matrix developer room and saw this, do any of you have neon.list with release in it instead of user?

I can confirm, looking at sources list I found that it was set to release.
That is strange is that I did a clean install on that machine and after installation I am pretty sure that it was set to user.
Actually as a workaround I did a new install as I use a separate /home partition. That's the way I discover that the qt 5.15 files were now not included in the user neon server