An interface/controls scaling slider doesn't exist in MATE. MATE Tweak does support switching between 1x (Regular) and 2x (HiDPI), but not fractional scaling like 1.5. This is because the underlying toolkit (GTK3) only supports full integers.
What @ugnvs describes will adjust the font DPI, an alternate to achieve a midway between 1x and 2x.
MATE Tweak does support switching between 1x (Regular) and 2x (HiDPI), but not fractional scaling like 1.5. This is because the underlying toolkit (GTK3) only supports full integers.