What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Shotcut version 20.07.11
Can you repeat the problem? If so, what are the steps?
If I select “replace” in the “playlist” or under “timeline” on the video via right click nothing happens. There is no dialogue or anything else.
As @Namna said.
Select a clip/image on the timeline or the playlist. The replace function will replace the selected clip with the clip/image in the source viewer.