Once you have the image you can save it straight to a data tables media column.
As for getting the image from the plot I have not tried this in Anvil but here is the plotly docs for exporting an image.
https://plotly.com/python/static-image-export/
You might have to use the uplink for this or choose another plotting package.
Realistically though the first step would be to comment out the plot code in your pdf form and confirm that is the reason for the time out.