After upgrading to GNOME 47 and enabling XWayland fractional scaling with the following command:
gsettings set org.gnome.mutter experimental-features "['scale-monitor-framebuffer', 'xwayland-native-scaling']"
Slide Show no longer works on LibreOffice Impress on 1.5x scaling.
Welcome to the community! 
Have you tried using an X11 session directly?
I tried to reproduce with a simple odp made in LO-still in Gnome 47 wayland at 150% – seems to work.
I haven’t used this.
I did not use a X11 session but I did try launching Impress with the Environment Variable:
GDK_BACKEND=X11
and then it seems to work fine.
This issue only arises when launching LibreOffice with native Wayland.
Did you enable xwayland scaling with:
gsettings set org.gnome.mutter experimental-features "['scale-monitor-framebuffer', 'xwayland-native-scaling']"
Because if I disable XWayland scaling the issue seems to longer persist.
Ya.
That’s strange. I switched to LO-still and still experience the same behavior when starting the slide show.
I should have added without Gnome extensions.
Even after disabling all the extensions having the same behavior.
Be more specific. Does not start by clicking or is it invisible?
The attached screenshot in the original post is what I see when I start the slide show. Notice how the Impress window is not focused? Because the slide show window is focused upon and it’s transparent regardless of any extensions used.
Ok so after troubleshooting a little more I found out that xwayland scaling doesn’t matter for this bug to show itself. Only enabling experimental fractional scaling is required with the command:
gsettings set org.gnome.mutter experimental-features "['scale-monitor-framebuffer']"