SharePoint Server 2019 September 2020 Public Update Bug Update15 Sep 2020 | SharePoint 2019
Microsoft has released workarounds for the SharePoint Server 2019 September 2020 Public Update bugs. There are actually two different bugs, one for the non-English issues surrounding Modern like the blank Command Bar and Site Contents, and a second around managing site collection and site level search settings.
For the Modern bug, the workaround is to use classic views. For search, using PowerShell to modify settings at the site collection and site level rather than the Site Settings UI.
These workarounds are documented in KB4484505.