Check it in ten seconds
df -h /System/Volumes/Data # before # …move something large to the Trash… df -h /System/Volumes/Data # unchanged
The number moves when you empty the Trash, not when you fill it.
Why this matters for cleaner apps
Most cleanup tools move things to the Trash — which is the right thing to do, because it is recoverable. The problem is what they then tell you. An app that reports "freed 10.4 GB" at the moment it trashes something is describing an intention, not a result. Your disk is exactly as full as it was a second ago.
The honest version: say moved, then measure free space before and after and report the real difference. If it did not move, say that too — something else may have been writing at the same time, which happens more than you would think on a machine that is busy.
And "empty the Trash" is not free either
Emptying the Trash removes everything in it, including things you put there yourself and meant to keep. A cleaner that offers to "empty the Trash for you" is offering to destroy files it never touched. The narrower, safer version is to permanently remove only the items the app itself moved, and leave the rest alone.
Photos work the same way
Deleting photos sends them to Recently Deleted for 30 days. Same trap, longer fuse: the space does not come back until that is emptied too.