Steps to reproduce:
Open any PDF file from the web (e.g. This textbook). Press the download button once the document is loaded. The file is named document.pdf.
The filename should match the original, for the example this should be LeeSeshia_DigitalV2_2.pdf.
Orion, OS version; hardware type:
Version 0.99.124-beta (WebKit 616.1.10)
(macOS Ventura 13.3.1 build 22E772610a) (Mac minia)