Window Mode

[slprice000]

I cannot find this  under the image menu bar?  I am running GIMP 2.10.20 (revision 1),

Help appreciated 

The GIMP user interface is now available in two modes:

multi-window mode,

single window mode.

When you open GIMP for the first time, it opens in single-window mode by default. You can enable multi-window mode unchecking Windows → >Single-Window Mode) option in the image menu bar. After quitting GIMP, GIMP will start in the mode you have selected next time.

[rich2005]

By default, Gimp will save the last settings before closing.

In multi-window mode the position of the windows is important when switching back to single window mode. If you do not like what you see use Edit -> Preferences -> Window Management then click on Reset Saved Window Positions to Default Values. That gives the single window arrangement same as a new install.

If you want Gimp to retain any particular Window arrangement, either single or multi-window:

Set Gimp Docks up exactly the way you want to start a new session.
Then Edit -> Preferences -> Window Management
Untick Save window positions on exit
Click on Save Window positions Now.