SUMMARY
When chrome-remote-desktop is running with an open session, it creates a display :20. In order to work properly, chrome-remote-desktop generally requires its own desktop environment running on its display. In this case, I am using cinnamon desktop for chrome-remote-desktop for :20 and KDE on the main display :0. Both sessions must be logged in as the same user.

Spectacle, when invoked using a shortcut or when loaded from the KDE menu from display :0, loads only on display :20. That is, the application window fails to load in the display and desktop environment from which it was invoked. When invoked from a terminal launched from display :0, the spectacle window appears correctly in display :0.

STEPS TO REPRODUCE
1. Install chrome-remote-desktop
2. Log into chrome-remote-desktop using cinnamon with software rendering
3. In the physical KDE login session, load spectacle from the menu or with the prtscn button.

OBSERVED RESULT
Spectacle doesn't appear in KDE on display :0 when launched from KDE, but rather appears on display :20.

EXPECTED RESULT
Spectacle should load on the display and desktop environment from which it was invoked.

SOFTWARE/OS VERSIONS
Operating System: Linux Mint 20.2
KDE Plasma Version: 5.18.7
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.11.0-44-generic
OS Type: 64-bit
Processors: 12 × AMD Ryzen 5 5600X 6-Core Processor
Memory: 31.3 GiB of RAM

$ cinnamon --version
Cinnamon 5.0.7

$ uname -a
Linux xxxx 5.11.0-44-generic #48~20.04.2-Ubuntu SMP Tue Dec 14 15:36:44 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux