SUMMARY
If the screen is dimmed after some time of inactivity (Dim screen option in Energy Saving KCM), and that a paused media is put on play with KDEConnect, then the screen stay dimmed and will get dimmer next time it stays inactive enough to trigger the dim.

STEPS TO REPRODUCE
1. Install KDE Connect, both on your desktop and phone
2. In Power Management → Energy Saving, set «Dim screen» to a low value (to ease testing)
3. Launch a video in a MPRIS-enabled player (e.g. VLC)
4. Pause the media
5. Wait for the screen to get dim because of inactivity
6. Put the media on play with KDE Connect

OBSERVED RESULT
- Screen brightness is not reset to its normal value.
- You can repeat steps 4. to 6. to get the screen dimmer and dimmer.
- Moving the mouse or typing a key reset the brightness to normal, either when the screen is dim or after it went into screen energy saving mode.

EXPECTED RESULT
Screen brightness is reset to normal if something like playing a video is blocking energy saving, even if no key has been typed and the cursor hasn’t been moved.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.14.2