The screen locker is broken and unlocking is not possible anymore.
in order to unlock switch to a virtual terminal (e.g. Ctrl+Alt+F2),
log in and execute the command:
loginctl unlock-session 2

Afterwards switch back to the running session (Ctrl+Alt+F2)

cat /etc/os-release
NAME="openSUSE Tumbleweed"
# VERSION="20210418"
ID="opensuse-tumbleweed"
ID_LIKE="opensuse suse"
VERSION_ID="20210418"
PRETTY_NAME="openSUSE Tumbleweed"
ANSI_COLOR="0;32"
CPE_NAME="cpe:/o:opensuse:tumbleweed:20210418"
BUG_REPORT_URL="https://bugs.opensuse.org"
HOME_URL="https://www.opensuse.org/"
DOCUMENTATION_URL="https://en.opensuse.org/Portal:Tumbleweed"
LOGO="distributor-logo"

uname -a
Linux my-opensuse 5.11.15-1-default #1 SMP Fri Apr 16 16:47:34 UTC 2021
(64fb5bf) x86_64 x86_64 x86_64 GNU/Linux

rpm -qa | grep ksc
kscreen5-5.21.4-1.1.x86_64
kscreen5-lang-5.21.4-1.1.noarch
libkscreen2-plugin-5.21.4-1.1.x86_64
kscreenlocker-lang-5.21.4-1.2.noarch
kscreenlocker-5.21.4-1.2.x86_64
kscreen5-plasmoid-5.21.4-1.1.x86_64

kdeinit5 --version
Qt: 5.15.2
KDE: 5.81.0

lscpu | grep Model
Model:                           142
Model name:                      Intel(R) Core(TM) i5-7260U CPU @ 2.20GHz

lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Iris Plus Graphics 640
(rev 06)