Both #i3wm and #sway let you turn titlebars on and off, also borders on, off, and varying thickness.
The only time titlebars are enforced is when you're using tabbing (so the tab is basically the titlebar), and of course, the stupid practice of Client-Side-Decorations, where you're getting a titlebar if you want one or not, because we're a cult and we know better than you, the lowly user. :eyeroll:
I sometimes use this to identify windows: https://codeberg.org/rldane/scripts/src/branch/main/displaywindowtitle