Also, just experimented, and, if the mixer window is open, keystrokes "alt" and "F4", hit together, will close it.


(Fender) Squier Vintage Modified '70s Stratocaster
Roland AC-60
Intel i7-7800x @ 3.5GHz, 16 GB RAM, AMD Radeon RX 580, Windows 10 Home 64 bit
Focusrite Scarlett 2i2 with Pro Tools First, BIAS Amp2, Bias FX Pro and BIAB2019 on dedicated 500GB SSD