Some scans, exports, updates, archive operations, and file changes need temporary working space even when the eventual goal is removal.
Confirm which volume is full. Move known personal files to verified storage, remove obsolete Downloads or installers, and empty Trash only after review.
Quit apps creating large temporary data. Pause active downloads and finish or cancel incomplete exports safely.
Do not delete unknown Library or system folders. Restart after recovering a reasonable amount of space so macOS can update its state.
If a disk remains unexpectedly full, check snapshots, cloud storage behavior, virtual machines, device backups, and application-managed libraries through their supported tools.