Correct, MLT is an XML file. If the MLT and the video files are in the same folder, or if the video files are in a subfolder relative to the MLT file, then Shotcut embeds relative file names in the XML and nothing needs to be done. Move the XML and video files together to your other drive and it will just work.
However, if the MLT references a file outside of its folder or subfolders, then Shotcut embeds an absolute file reference. Edit the XML with a text editor and do a search and replace to change the drive letter. Regular expressions are useful but usually not necessary for this. The (better) alternative is to move the video files into the MLT folder, then edit the XML to strip out the absolute reference and turn it into a relative one.
Example: Look for
<producer> elements that represent each clip on the timeline, and inside them should be elements that look like this:
<property name="resource">E:/Projects/Drone Flight/MyVideo1.mp4</property>
To make them relative, move the MP4 files to the folder with the MLT file, and change the elements to look like this: