I have tried pasting the asset link from my webflow assets into the Open Graph Image URL as other threads have suggested, but when I share my site link, it shows the first image that appears on my website as the thumbnail - which is not what I want. It appears the asset link is just being ignored but not sure of any other way to change the thumbnail when I share links.
That generally means your og:image is not compliant with the service you’re trying to share it on. Read up on the services you’re targeting, they change regularly.
In particular;
Image size, usually has to be a minimum width and height for most services
Image aspect ratio is very specific on some services, e.g. 2:1
Image file format, e.g. I believe LinkedIn still does not support webp
