It's not really a solution but today I tried to install Arena with the Epic Games Launcher and it works. I got the same issue I had some months ago that Arena freezes when you try to exit and then I need to force exit but that's still better than not being able to install Arena. (Support told me then that I need to deinstall Arena from the Epic Client and install it directly from them)

I got the same problem. I tried the troubleshooting article but got stuck on uninstalling Arena where I got the same message that another installation is in progress. Even with Revo Uninstaller was I unable to uninstall Arena.

I've been doing the same. PC tries to run MTGA installer and says "updating 1 of 1..." then "updating 2 of 1..." then flips back and forth, then tells me to contact support. Have scraped every bit of my computer for MTGA data, and have installed to different disks with no luck. Works on my old laptop, but not my desktop. Very annoying bug that prevents me from playing the game.