For me, desktop UI peaked at Windows 98.
Installing the 95/98 GTK theme by B00merang is one of the first things I do after a fresh installation of Linux Mint.
I do try other themes once in a blue moon. But I soon realise it is a downgrade and revert back. The last theme I tried was the Arc theme back in mid-late 2010s.
I never found that to be a problem. In fact, I find the thumbnails distracting. But I can see it being a problem for others.
The rare occasion I work with image files, I just open it to identify, if I haven’t already named it properly.
It also helps that most of my workflows are not image-heavy.