In PowerPoint, you can just select everything, then right-click -> save as image, and it saves whatever you have selected rather than the whole slide. There doesn’t seem to be a way to do that in Impress, but I realised you could copy-paste into Gimp and that would copy the objects as an image, so I’ve been making memes that way.
The issue is that the slide size isn’t going to match with the meme size and there’s no way to predict it. … unless there’s a workaround that I’m not aware of. I’d need it to ignore the slide size and only include the images. The only way I found I could do that in libre office is to highlight and copy/paste.
In PowerPoint, you just highlight all images->right click->save as picture and that works just fine.
I guess I’ll just have to work the courage to make feature requests, or better yet, understand open source code to make improvements.