1. You can configure the keyboard shortcuts in KDE. Or use something like Toshy: https://github.com/RedBearAK/Toshy

2. KDE Autostart

3. KDE Discover. Supports flatpak for example: https://flathub.org/en

4. SysD Manager (https://github.com/plrigaux/sysd-manager). Can be installed from Flathub. SystemdGenie is another one.

5. KDE Plasma System Monitor

6. KDE User Manager