On Linux this depends on your theme really, all the themes i use have scrollbars - e.g. here is an example with Gtk3 (which IIRC introduced the "autohiding scrollbars" to Linux desktop)[0]. It is "cdetheme-solaris" which i think is from [1]. I might have modified it a bit though. Though normally i use Gtk2 apps with a modified "cleanlooks" theme (a screenshot from Lazarus[2] i made a couple of days ago shows it - including the scrollbars :-P).

[0] https://i.imgur.com/CAyu5Ay.png

[1] https://github.com/josvanr/cde-motif-theme

[2] https://i.imgur.com/Yw1tTcD.png