I’m using Manjaro Gnome, Gnome Shell 43.2, GTK 3.24.36, Tweaks 42.beta on a desktop pc. Legacy (GTK3) Theme Scheme Auto Switcher installed and enabled.
Logged in with Gnome I get a top bar as I like it, although in other respects I prefer Gnome classic. But that gives me a top bar I dislike, but am unable to change. I have searched a lot and tried many different things, without success. Eventually I found this post, which perhaps explains the difficulty:
"Gnome 42 adopted a new version of its graphical toolkit, GTK4 with its libadwaita library. GTK2 and GTK3 themes do not work with GTK4.
Because of this move, applications that “still” use GTK3 (currently still a vast majority, including even Files 42.0) and even GTK2 (The Gimp still does) are now considered - and labeled as - Legacy applications."
So…
Question 1: Should I update GTK to the latest version, or will that cause problems elsewhere? And if I should, how do I update GTK? (Most of the info google brings up is either very out of date or unintelligible to someone with my level of knowledge.)
In the course of my troubleshooting I attempted to change my shell theme, but again I couldn’t, which alerted me to a possible issue in Gnome Tweaks: for Appearance > Themes > Shell there is only Default shown in the drop-down menu. When I click on the <(None) [open folder icon]> button to its left, Files brings up the “Recent” files list in the Select-a-theme window. I can then go from there to /usr/share/themes where i find loads of themes listed, but clicking on any of them does nothing.
Thus…
Question 2: How can I change to a different shell theme?
(And is something amiss with the attempt I described above?)
You already have the latest versions of both gtk3 and gtk4. 
Perhaps find a custom theme that is compatible with GNOME 43 on Gnome-look.org. If you do, keep in mind that you will need to install gnome-shell instead of gnome-shell-maia.
Thanks, but …
how come gtk4? The only system info I found says it’s GTK 3.24.36 (and now I can’t find where I saw that!)
I’m not so much keen to change the shell theme, just get the current one to work. It surely can’t be right that nothing out of all those themes in the folder is compatible, or that the wrong folder opens when I click to find an alternative: that’s just bad design isn’t it? See screenshot for what my top bar looks like and why I want to tweak it:
Hi Nickdc,
to get proper help you should post some info from you system.
You can post the result of " Inxi -Fzya " command for this (for future posts).
This will give us the information from your system like versions… so that people can help you.
On the other hand, regarding the themes, you can check if you activated the in the extensions tool the extension “user themes” this will allow you to use themes installed that are not the “default”.
In the website Yochanan provided previously in this post you can find them in the correct section, so when you install them they can be used.
Your current theme might not work because of compatibility issues with the new libraries, the theme you use must be compatible with your gnome version, suggest you to go over the theme website and have a look.
Gnome has a certain way … There’s nothing to be done in that regard.
The best course of action is to live with it - it requires the least amount of energy.
Hi, and thanks for your advice. In the past I have posted more comprehensive info on my system; this time I thought I’d provided enough for starters, but point taken.
I do have “user themes” activated, but changing from “default” to “Gnome classic” doesn’t appear to make any difference. It’s not a deal breaker and I’m inclined to take linux-aarhus advice and live with it: there are more important things to obsess about! It’s just every now and then I like to have a little tinker and see if I can iron out another little glitch that creates low level annoyance.