This was not worded like this 24 hours ago.
When upgrading Delivery Controllers to Citrix Virtual Apps and Desktops version 1912 or 2003: Upgrading SQL Server Express LocalDB is optional. Local Host Cache works properly, with no loss of functionality, regardless of whether you upgrade SQL Server Express LocalDB. We added the option to move to a newer version of SQL Server Express LocalDB in case there are concerns about end of support from Microsoft for SQL Server Express LocalDB 2014.
When upgrading Delivery Controllers to Citrix Virtual Apps and Desktops versions newer than 2003: The minimum supported version is SQL Server Express 2017 LocalDB Cumulative Update (CU) 16. If you originally installed a Delivery Controller earlier than version 1912, and have not replaced SQL Server Express LocalDB with a newer version since then, you must replace that database software now. Otherwise, Local Host Cache will not work.