This uses the “filter sets” feature - you need Shotcut version 23.05.14 (and up) to use filters sets.
Method -
Unzip and install the two filter set files into the Shotcut AppData folder*
On the timeline - add two transparent tracks - 6 seconds or more.
Apply JR-mirror-text-TOP-V3 filter set to top track,
Apply JR-mirror-text-BOTTOM-V2 filter set to bottom track.
Done.
*If you don’t know how to do this, @musicalbox gives clear instructions in this post: