SUMMARY
Basically, the panel scripting thingy documented at https://userbase.kde.org/Plasma/How_to_create_a_Unity-like_look_and_feel_theme_using_Plasma%E2%80%99s_Desktop_Scripting_API has 0 way right now to give a newly birthed panel the Floating attribute, nor any of the non-default Adaptive Transparency values, despite everything I've tried (likely because of its positioning of the configs in plasmashellrc instead of plasma-org.kde.plasma.desktop-appletsrc).

Even Global Theme Explorer's layout saver cannot save those attributes on panels.


STEPS TO REPRODUCE
1. N/A

OBSERVED RESULT
The inability to pre-set floating or solid/transparent adaptive transparency options in panels in Desktop Layouts

EXPECTED RESULT
The ability to pre-set floating or solid/transparent adaptive transparency options in panels in Desktop Layouts

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: KDE neon 5.25
(available in About System)
KDE Plasma Version: 5.25.3
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.5

ADDITIONAL INFORMATION
Two fixes I can think of are: Either move the configuration over to the plasma-...-appletsrc file instead of plasmashellrc, or allow scripting to change the values, for newly created panels we store as variables in our desktop-generation script, in plasmashellrc as well.