late to the party, but I had OperaGX do a clever evil thing recently - I have an old machine running MacOS 10.14 (for reasons), I had GX up, and I alt-tab'd and noticed there was the "don't symbol" (ghostbusters) over the OperaGX Icon. I thought, "that can't be right". I'm running GX right now. I double checked, and I was using GX with several windows open. But the symbol was right - they had Updated OperaGX that I WAS running, WHILE I was running it, to a version that WOULDN'T work on the computer I was on. I eventually restarted GX, and got a 'You can't use OperaGX with this version of MacOS". Jerks.
I dug around, and very roughly, the .app file is not the App. They use a folder off in Library to store the actual pieces of the app, and it there is a few different pieces, and the .app file points to the actual executables.
Anyway it was fun while it lasted. Never again.