Is there a possibility to define multiple touchbar's for one app

I would like to switch to a different touchbar layout depending on the current mode of the app.
Is this possible (not automatic but at least manual ) ?

What kind of mode / what are you trying to do?
You can always create groups or conditional activation groups, but it really depends on the use case what works best.

e.g. the app has a view and an edit mode.
In both modes you have mode-specific commands that you can use.
So I want to switch the touchbar between a view layout and an edit layout.

Then I'd just create a group/folder inside the Touch Bar config of that app. You can use the predefined action "Open Touch Bar Group" with name and assign it to any trigger (e.g. keyboard shortcut) in BTT.

Great - works as expected.