SUMMARY

With adaptive sync set to automatic, whenever I would fullscreen any app, whether it would be an xwayland app, a qt app, a gtk app or firefox, it would cause the display to turn itself off as if there was not any output, and shortly come back afterwards, not giving it enough time to consider that there is no signal and try to switch to another input source. Any sudden mouse movements would cause it to flicker again.
I then set the adaptive sync to 'Always', and that has caused the display to have this behaviour constantly, regardless of whether there was a fullscreen window present or not. Switching to 'never' has resulted to this behavior not occurring. The allow screentearing for fullscreen windows option did not affect this whatsoever.

STEPS TO REPRODUCE
1. Connect external display to laptop via HDMI.
2. Close laptop lid.
3. Ensure adaptive sync is set to "Automatic".
4. Fullscreen anything, e.g. a youtube video.

OBSERVED RESULT

Display flickers black.

EXPECTED RESULT

See my content normally.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 6.7.3-x64v3-xanmod1
(available in About System)
KDE Plasma Version: 5.93.0
KDE Frameworks Version: 5.249.0
Qt Version: 6.7.0

ADDITIONAL INFORMATION

Built-in laptop display does not have adaptive sync.
16 × AMD Ryzen 7 5700U with Radeon Graphics
AMD Radeon Graphics
External Display is Acer Nitro VG271U