RAM memory alwa

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 current metrics for RAM usage, shown in the "Memory" tab of Activity Monitor (in your Utilities folder) are “Memory Pressure” and "Swap used." In this real-world example, the computer has 12GB of physical RAM and, applying pre-2013 metrics to the 11GB “Used,” appears to be 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.

See: Check if your Mac needs more RAM in Activity Monitor - Apple Support

If a 21.5-inch iMac seems slow, based on hundreds of reports here there is a 95+% chance that it is NOT RAM but the glacially slow mechanical hard drives Apple used in base-level 2012-2019 21.5-inch iMacs. All the RAM in Texas can't make a slow hard drive faster.

Please read Writing an effective Apple Support Communities Question and then re-write your question with some specifics. We are pretty good but we need your help with some specifics about the iMac you own, they have been in production over 20 years in hundreds of configurations and you have not described what the problem is or what troubleshooting you have tried.

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community

Hard to say with no details at all. Apps use memory, so my guess is you have too many running or some apps are using an excessive amount. Chrome Browser can be a memory hog.