On the magic the gathering Arena MTGA forum they are reporting there will be scheduled maintenance, there will be no downtime during the 30 or so minutes it will take however you will have to update on your next restart of the game.
they will be making some repairs to the game installer hopefully they can resolve issue many have had with the installer failing on some devices and set up .
here is the Orginal post and link
magic the gathering Arena MTGA maintenance
We will be performing scheduled maintenance on March 4th, 2019 at 2PM PT (22:00 UTC) to deploy updates to the Magic: The Gathering Arena game installer. Maintenance is expected to last approximately 30 minutes.
There is no downtime with this maintenance, however players will need to update Magic: The Gathering Arena the next time the game is launched.
Patch notes will be available once maintenance is complete. magic the gathering arena