Maybe you can accept the results as-is (but make sure it's on the Query side), then use the properties in a Form or Report to make it a hyperlink again.
The reason why this happens is because, as Microsoft documentation
says, LCASE() function
returns a string
Functions always officially return
something. Have to pay attention to what that something is.
This is another one in the dozens of scenarios that prove you should not use creative datatypes (like Hyperlink) in a database - including in quasi-databases, like MS Access. Store it as plain text and worry about the fancy stuff when working with the
presentation layer - forms, reports, etc.
Query your text field as LCASE, then fancify it later.
Don't use formatting concepts at the table level - ever!