Created attachment 179946 [details]
Video of the bug

SUMMARY
If you draw a long stroke or line with spectacle (holding down the left mouse button) over a screenshot for long enough, Spectacle will start lagging more and more, and it can go up to a complete freeze of the application.

Tested on two different PC's, one with an R7 5800x3D and one with an i9-13950HX, strangely the lag is MUCH worse on the AMD system, while on the intel one, it still happens but only after a much longer stroke.

STEPS TO REPRODUCE
1. Take a screenshot with Spectacle
2. Select the standard Pencil
3. Draw a long stroke / scribble without lifting the left click

OBSERVED RESULT

Intense lag even after relatively small drawing

EXPECTED RESULT

No lag at all / not that much lag only after a couple of lines
SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION

It seems to start lagging WAY faster on my AMD system than my intel one.