I am using Apple MacBooks and macOS since 2010y I have been pleased all almost all the time.
However, I have never encountered something like “Your system has run out of application memory”, I think. Until I upgraded to macOS Catalina 10.15.1
I run a machine with 8GB of RAM. I wonder where the OS consumes 7.5 GB of RAM though.
Something worth a “screenshot” to remember…