Welcome,
as a beginner I also did make a lot of slideshows with Shotcut.
The keyframes do make repeatedly trouble in slide shows if you change the zoom + offset, use a different aspect source photos or have to zooming over time on.
I do recommend to you prepare your photos with e.g. darktable and crop it to the exact pixel numbers before including them to Shotcut.
It is also better if you want to reuse some of the photos in another video.
If you disable the zooming effect, too you do not get troubles with keyframes anymore.
Normally if you cut a keyframe away it zooms out to 0%.
With a double click? on the watch in the zoom filter widget you can easily disable the keyframes for the selected video, too!
This video was fully edited in Shotcut by me without preparing it with darktable and the keyframes did cost me a lot of time!