Windows drive letters aren't restricted to A-Z; the subst command allows creation of aliases like +:. Drive letters function as symbolic links within the NT namespace, with paths converted by certain APIs. While alternatives exist for drive letters, applications like File Explorer and PowerShell only recognize A-Z letters, limiting usability. Non-ASCII drive letters are technically possible, yet may yield inconsistent behavior across different applications and APIs, leading to potential encoding issues.
https://www.ryanliptak.com/blog/windows-drive-letters-are-not-limited-to-a-z/