Clicking on the text in the image window with the Text tool will automatically select the top most layer if text layers are covering each other. There's no option for the Text tool to ignore other unselected layers. There are workarounds of course.
The easiest way to start editing a text layer covered over by another is to select the Text tool, then double click the layer you want to edit in the layers panel. The text box will automatically open for editing.
Another method is to temporarily hide the layers you don't want the tool to select, using the Eye icon in the layers panel. Then you can freely edit the visible layer, or create a new text layer without interference.
Also you can create a new text layer off the edge of the canvas. No need to use the text tool inside the canvas area. Once you have made the new text layer you can move it's position using the Move tool.
Note that if you find yourself working with a lot of text layers, GIMP might not be the best software for that. Better perhaps to use a vector image editor like Inkscape, or page layout software such as Scribus. Both of these are free and open source like GIMP.