I believe you are applying pre-2013 standards to how modern Macs use RAM. Starting with macOS 10.9 "Mavericks" (Oct 2013), Apple changed memory management to a new system to make better use of RAM and allow faster access. One of the tenets of this change is "Free RAM is wasted RAM" so the OS stages RAM for quicker availability.
The new metrics for RAM usage, shown in the "Memory" tab of Activity Monitor (in your Utilities folder) and "Swap used." In this real-world example, the computer has 12GB of physical RAM and, using pre-2013 metrics, looks like it is in deep trouble:

However, the true situation is shown in the fact that Memory Pressure is nil and Swap used (a measure of Virtual Memory usage) is zero. And, at the time that chart was generated, the computer worked without issue.
Cleaning RAM? Using a third-party solution only interferes with the automatic maintenance systems you paid Apple to build into the OS. The macOS has, like a cat, been cleaning itself nicely for nearly 20 years. Adding third-party stuff is an invitation to poor performance.
Is Swap is high, a simple restart will clear all that without the need for outside apps.
If you have a lot of third-party add-ons, it would be a good idea to post an Etrecheck report. It looks for software issues and displays RAM and drive performance without revealing any security or personal information. It is free in the Mac App Store. Please use these instructions so the report posts cleanly and legibly:
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