After the installtion of Cumulative Update 07-2021 KB5001975 – Sharepoint 2019 on-prem you have some problems. The content and structure of the site contains the “Documents” library, but when you try to open the library, a blank page is displayed. A blank page is also displayed when clicking on the “Site Content” link (/_layouts/15/viewlsts.aspx)
You can fix it by installing the patch KB5001974. Because KB5001974 need to be installed along with the KB5001975. The blog announcing the July 2021 CU for SharePoint Server 2019.
The blog states “Important: It is required to install both fixes [KB5001974 & KB5001975] (language dependent and independent) to fully patch a SharePoint server. This applies also to servers which do not have language packs installed. The reason is that each SharePoint installation includes a language dependent component together with a language independent component. If additional language packs are added later (only) the language dependent fix has to be applied again.”