Log into the Lucidchart in a browser tool and navigate to https://app.diagrams.net/tools/lucid/import.html into another tab.
Once authenicated you can convert all diagrams in your Lucidchart account to draw.io and output the results to one zip file.
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Diagrams.net and Draw.io Importer is a free Productivity Extension for Chrome. You could download the latest version crx file or old version crx files and install it.