Hello,
there is no setting in PDF24 for this. PDF24 uses the temporary folder that Windows provides for your user account (set by the Windows environment variables TMP and TEMP) and creates the subfolder PDF24 in it. If you set TMP and TEMP of your user account to a folder on the other drive, PDF24 uses that folder as well. Please note that all other programs then use this folder too, and sign out and in again so that the PDF24 programs pick up the change.
A PDF24 setting for its own temporary folder is on our to-do list.
Compress PDF is also available online: https://tools.pdf24.org/en/compress-pdf