Your Computer Is Low On Memory

I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to diagnose and identify issues, both hardware and software. It is trusted by many users. Please follow the steps outlined below:

1. Navigate to: https://etrecheck.com and get the free version of EtreCheckPro.
2. Download it. It is a free and trusted app. It is often recommended here on Apple Support Communities. 
3. Open EtreCheck, and before running the report, be sure to check “Allow full Drive Access” at the bottom of the EtreCheckPro window.
4. Run the report, and put it in a post, as seen here: https://discussions.apple.com/docs/DOC-250000211. We will then examine the report for issues in your Mac.

Cheers,

Jack

Boot into Safe Mode, and try EtreCheck again > How to use safe mode on your Mac - Apple Support

The Mac can be substantially slower while booted in and running in Safe Mode.

If the message is "Your system has run out of application memory", then this is caused by 1 of 2 things

a) your boot disk/SSD has run out of free space, and macOS can no longer create page/swap files for moving the contents of virtual memory from RAM to disk.

b) you have processes consuming huge amounts of virtual memory (most likely background agents or daemons). Every page (4K) of virtual memory requested requires a kernel address space resident page table entry. If a process (or set of processes) requests sufficient virtual memory address space, eventually these page table entries will consume so much RAM in the kernel address space, that the kernel will decide there is no enough RAM left over to run your applications. It will then pop up the "Your system is out of application memory" and list a bunch of innocent apps.

When this happens, run Applications -> Utilities -> Activity Monitor -> View (menu) -> All Processes -> Memory (tab) and see if you have some processes consuming huge amounts of memory (multiple gigabytes). If you do, those are the guilty parties. You can use the Activity Monitor (X) button to kill the memory hog processes.