"System has run out of application memory" Question (includes EtreCheck report)

In addition to what John Galt has advised, even though CleanMyMac was just installed today it will not do you any favors. Not surprised by the High CPU use warning from the app as well as the Kernel Panic that occurred today as well.

You are definitely just buying time and will eventually be needing a newer Mac. Read/Write speeds on the HD are pretty dismal to what you will find on any newer machine coupled with the large number of Page Swaps due to limited memory is dramatically slowing your machine down. You will see a huge improvement in speed with a newer Mac and will not be disappointed. It has served you well for a 10 year old machine, so no disrespect.

4 GB RAM isn't much these days, especially if you are required to use Google. You can see for yourself it's one of that Mac's most resource-demanding processes. That is not unusual, but Google is constantly updating itself and its demands will always increase, placing ever-increasing burdens on hardware that cannot be upgraded.

If you want to extend that Mac's useful life then uninstall Google. If you are required to use Google, consider getting something other than a Mac such as an inexpensive Chromebook or Windows PC that you can replace every couple of years to keep up with whatever Google requires of you.

I do not know what "mac.exe" is but it also appears to be a burdensome process.

I suggest opening Activity Monitor and selecting the Memory tab. Leave it open and running while you go about your usual business. If Activity Monitor's unitless Memory Pressure graph spends any time in the "red" it's a clear indication that Mac can't keep up:

Check if your Mac needs more RAM in Activity Monitor

Its SSD is also showing poor performance which is unusual. Run EtreCheck again and see if that complaint persists. 250 GB isn't an enormous amount either these days, but it appears to have more than enough free space.

In any case, yes that Mac is showing its age, and the effects of its fairly modest configuration are becoming apparent. If you want to keep it going you will have to keep doing what you've been doing: reducing the demands being placed on it to the greatest practicable extent. Google and Microsoft have never been shining examples of lean, efficient code.