
Hi @Tom Molskow,
Please check if your site is a subsite. The parent site is http://server/sites/topsite
and the child site is http://server/sites/topsite/subsite1
.
"SharePoint Server Publishing Infrastructure" require a Site Collection level feature when enabled impacts every site in the Site Collection. If you are in a subsite, you can active the feature in the tpsite of the sitecollection.
Currently there is no direct replacement of Content Query web part available in modern experience out of the box web part. You will have to develop the custom web part on your own. You can develop custom web part for modern experience using SharePoint framework (SPFx).
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