One website that offers a large selection of legal Commodore 64 downloads is the Internet Archive. The Internet Archive is a non-profit organization that works to preserve and provide access to historical and cultural works, including a wide variety of computer software. The Internet Archive’s collection of C64 software can be accessed through the Internet Archive’s website at: https://archive.org/details/softwarelibrary_c64
Other websites that offer legal C64 downloads include:
C64.com: This website offers a variety of C64 games and other software that have been made available for free download by their copyright holders.
CSDb: The Commodore 64 Scene Database (CSDb) is a community-driven website that includes a large collection of C64 software, including games, demos, and utilities. Some of the software available for download on CSDb may be freeware or shareware, while others may be available for purchase.
The Homebrew C64 Software List: This website is maintained by the Commodore 64 Homebrew Scene and includes a list of C64 software that has been released by independent developers or hobbyists.
It is always important to respect the copyright holders of software and only download or use software that you have obtained legally.