If your og:image isn't appearing on Facebook / Twitter / LinkedIn / etc, there are three likely causes-
Facebook's Sharing Debugger, and OpenGraph.xyz are two good tools to use here. FSD provides some diagnostic data, and OpenGraph XYZ will give you a good idea of how your link would appear on a range of services.
Visit both, paste in the full URL of your shared page, and see what it shows you. NOTE: FSD sometime requires you to click Scrape Again. to get current data. Check the "last scraped" timestamp it shows to know for certain.
If you're not seeing an image, is it because you do not have an og:image meta tag? If you have a tag, but your image is still not showing, then it might be too small for use.
If you're seeing your image fine, and it look as espected in both tools, than you can skip to STEP 3.
It's actually challenging to do that in the browser, so we'll use a simple online tool for this as well.
Get your og:image file URL, and open it in a new tab to make sure you actually see the image you want.
Now lets check the size...
Use Free Online Tools to see the size.
For it to display in most services your image must be 1200px x 630px minimum, and an aspect ratio of 1:91:1.
Each service has its own cache and tools for this;
NOTE: If you're having problems specifically with LinkedIn, make sure you're using PNG or JPEG format for your open graph image.
Linked in does not appear to support WEBP yet.