Your finger slip, up-graded Gimp 2.10.12 to Gimp 2.10.20, quite a slip 
and what you have are tool groups rather than individual tools. This does make sense considering the number of Gimp tools. You can revert from Edit -> Preferences -> Interface -> Toolbox as https://i.imgur.com/sH8dMrW.jpg
edit: You can not see the tool options because you have the Images tab active, use the left hand tab which is tool options
Your preferred layout is rearranged by closing / moving tabs around the docks.
A sort video on that https://youtu.be/01PeLL1F8Kg
More on setting Gimp up for the sort of layout you want https://www.gimp-forum.net/Thread-Fit-Gi...75#pid8475
The black theme is changed in Edit -> Preferences -> Themes
Icons changed in Edit -> Preferences -> Icon Theme
By default Gimp 2.10 uses single window mode, for the older multi-window mode use Windows -> un-tick Single Window Mode.
I really do not know why Windows users think that continually re-installing applications ever fixes anything
and what you have are tool groups rather than individual tools. This does make sense considering the number of Gimp tools. You can revert from Edit -> Preferences -> Interface -> Toolbox as https://i.imgur.com/sH8dMrW.jpgedit: You can not see the tool options because you have the Images tab active, use the left hand tab which is tool options
Your preferred layout is rearranged by closing / moving tabs around the docks.
A sort video on that https://youtu.be/01PeLL1F8Kg
More on setting Gimp up for the sort of layout you want https://www.gimp-forum.net/Thread-Fit-Gi...75#pid8475
The black theme is changed in Edit -> Preferences -> Themes
Icons changed in Edit -> Preferences -> Icon Theme
By default Gimp 2.10 uses single window mode, for the older multi-window mode use Windows -> un-tick Single Window Mode.
I really do not know why Windows users think that continually re-installing applications ever fixes anything