reducing the space between staves

There are two ways of doing this.
Method 1: Go to Format - Style - Page and disable vertical justification of staves. That should give you enough space for your frame.
Method 2: Go to Add > Frames > Append vertical frame. Select this and drag to move the staves up closer together. You can then Right-click in the box and choose Add > Text.
You can combine the two methods if necessary.

See the Handbook: https://musescore.org/en/handbook/3/layout-and-formatting#style-page

Is this what you are hoping for?

Sunset Lake- anonymised WITH NOTE.mscz

This is what I did.

1. Click on the horizontal frame after the last measure
2. Add>Frames>Append Vertical Frame
3. Click inside the new frame and select Add Text from the dropdown
4. Type your text
5. In the inspector select Frame - Rectangle
6. In the inspector adjust the margins and thickness of the surrounding rectangle to your taste
7. In the inspector change the text font to a monospaced font and select an appropriate size. I used Deja vu Sans Mono. A monospaced font makes adjusting the layout easier as all the characters and spaces are the same width. This is necessary as Musescore does not have the facility to use tab stops
8. Add leading and trailing spaces to each line to achieve the layout you want. The trailing spaces are necessary to put a gap between the right hand edge of the box and the right hand edge of the text
9. Adjust the placement of the note by clicking on the edge of the frame and adjusting the various sizing options in the inspector.

Alternatively, if you can create the text as an image (png, jpeg or svg format) you can add that to the frame you created in steps 1 and 2 above. You can then adjust the size of the frame as in step 9 above.

Unfortunately Musescore does not handle formatting of text very well. That means there are more hoops to go through than one would think necessary if you want things like columns and indentations.