magento2 – Magento 2 – How to find out where certain blocks are defined?

I try to remove some blocks on the 404 site:

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but I have no idea where they are defined.
I searched in the layout file vendormagentomodule-catalog-searchviewfrontendlayoutcatalogsearch_result_index.xml and searched other catalogsearch_result_index.xml files but I am unable to figure out where these are defined so I can remove them.