Is this site "https://x-mouse-button-control.fr.uptodown.com/windows/telecharger" a safe site to download from?

well what are you trying to download?

idk about that but here is a safe site https://www.highrez.co.uk/downloads/xmousebuttoncontrol.htm

NOTHING from uptodown, softonic, and other bad sites are safe.

basically download at ur own risk