Short answer:
- Open Source Initiative (OSI) Approved Licenses – the authoritative list of licenses that meet the Open Source Definition: https://opensource.org/licenses/
- SPDX License List – the canonical, machine-readable catalog of license texts and identifiers used by tooling: https://spdx.org/licenses/
Related, but not “the” canonical OSS list:
- FSF Free Software Licenses (free software perspective): https://www.gnu.org/licenses/license-list.html
- Choose a License (curated guidance, not exhaustive): https://choosealicense.com/licenses/