Shopware 6 redirect module. In case of 404 try to find a redirect url for products and later for categories.
Put a CSV with the old urls and skus in the following folder: var/loewenstark/redirect/url_export.csv
To export the URLs from Magento the following tool can be used _exportTools/magento/products/url_export.php
The format of the csv is: id;sku;url
e.g. 123;12-345;https://example.com/old-product-url
Not yet implemented.