Welcome to the forum!
If you're using File menu > Export PNG the only reason the image would not show up, is if you accidentally exported a blank area of the page. Be sure to pay attention to the 4 buttons at the top of that dialog. They allow to export the entire page, the entire drawing, only what it selected, or some custom area.
Don't use File menu > Save As > cairo png, to export a PNG.
For using File menu > Save As PDF, it could be the same reason, if your drawing is not inside the page border. If the page border is not showing, you can make it show up from Document Properties > Page tab then down near the bottom there's a checkbox for the page border. If you don't see the checkbox, you might need to temporarily dock that dialog, if it is floating (not docked). (It's a small bug in a large dialog on smaller screens.)
There could be other reasons why it's not showing after saving as PDF, but it would be hard to say exactly what the reason is, without being able to see the image. One reason could be if you didn't not check "rasterize filter effects" in the Save As PDF dialog. But there could be other reasons as well. You're welcome to share the SVG file with us. SVG is better than PDF or PNG. You can attach it to your next message, or upload it anywhere, and give us the link.
Unfortunately, I'm in a bit of a rush at the moment. So if you can't sort out docking the Document Properties dialog, try Help menu > Inkscape Manual. There's a specific section of a chapter on docking. Use the Comprehensive Index and click on either Dialogs or Docking (I'm not sure at the moment which one).
Hopefully I can check back in this evening, or maybe someone else will happen to visit shortly.
Oh, well look at that! 2 messages while I was typing!