As Unix OS (What Mac OS is) expert, I can’t see how this app does anything.

Memory is allocated by the OS, to run the PC. Memory is allocated, as apps request, by the OS. Unless the OS developers at Apple have made a very serious mistake in OS design, and over the last decades since Jobs brought Unix to Apple, there is no possible way that memory can be left, unattended and unusable (The OS automatically frees all memory, once an app dies, quits, exits gracefully, or crashes). This tool cannot do what it claims.

RealGlaird about Memory Clean - Monitor and Free Up Memory, v6.2