On KDE you can just type a number into the scale percentage field in the display configuration settings pane. I typed "73" and it snapped to 72.5 which is probably close enough.
I don't know whether GNOME supports anything similar, unlike KDE they really don't like giving users very many configuration options.
Weird, mine lets me go down to 50%: https://files.catbox.moe/gjuzl6.png . Out of curiosity, do you use an nVidia graphics card? I know in the past their drivers have had problems with scaling on Linux.