Part 1 of 2
There is Purgeable Space and there is Empty Space.
Purgeable Space which is Controlled by the Operating System.
When the Operating Systems decides the computer needs additional Empty Space, it will move a portion of the Purgeable to Empty space
AFAIK - there is no User Actions to hasten this transition from Purgeable to Empty Space
It can day or longer before this will occur
Part 2 of 2
If Apple Intended there to be a way for the user to Clear Purgeable Space - they would have included instructions to perform this action - IMHO
Any Third Party Applications that will interfere with the normal operation of the OS, is an invitation for disaster.
Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale. What the Application may do to the computer is up to the User to check this out before purchase
Any of the below should be removed Developers Instructions and or never installed on this computer at all
1 - Disk Cleaner
This will include CleanMyMac , aka “ BrickMyMac “
MacKeeper,
Dr Cleaner Pro Plus
Open Cleaner one Pro
Macmechanic
Read some of the posting and arrive at your own conclusions.