Not really surprising, but a bit frustrating that while a third-party theme (Gnome Extension) can be used, the case of security-drive applications like Timestamp and the Synaptic Package Manager, they don't react to such themes in whole or in part. In using a theme that is based on the appearance of Mac OS "Mojave", these two programs remain in the default mode of Pop!OS 22.04 to "light" instead of the dark mode that is set with "WhiteSur-Dark" that applies to most everything else.
Oddly enough while these apps remain in light mode, their window buttons work in accordance with the WhiteSur-Dark appearance as set up in Gnome Tweaks.
Equally strange are a few apps like Firefox, which retains the Pop!OS 22.04 window buttons rather than the Mac styled ones. While my other browser (Brave) render the Mac window buttons just fine.
And while the WhiteSur-Dark mode is applied in the "appearance" setting of Gnome Tweaks, if I access the Pop!OS display settings, it remains locked in light mode, reflecting those exceptions like Timeshift and the Synaptic Package Manager that also remain in light mode.
Of course with a simple change in Gnome Tweaks, if I change the appearance from WhiteSur-Dark to Pop-Dark, all applications conform to the dark mode. Though the window buttons also revert to Pop!OS, which are not quite as elegant as the Mac OS equivalent.
I suppose the only thing left to ponder besides replacing the entire theme package (if this is just a programming glitch) is whether or not the light or dark appearance for Pop!OS can be locked using the dConf Editor? I'm not sure...but just wondering if it would circumvent apps like Timeshift and the Synaptic Package Manager to show up in the dark mode along with everything else?
The more I think about it, it would seem the best thing to do is to simply switch the appearance setting in Gnome Tweaks to "Pop-Dark" which would make ALL apps working properly in dark mode, as well as a consistency of ALL apps having the same windows buttons.