system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] How powerful or devastating are those portals, made by Strange or Wong, when they are closed?

I'm talking about those portals used for fast travel or teleportation.

They effectively cut off Cull Obsidian's hand when a portal closed.

Could they not have done this to decapitate Thanos or cut off his glove?
gpt
Yes, Strange should have been able to cut off Thanos' hand using the portal. However, there are three caveats.

One, Strange might have simply not thought of it. When Wong cut off Cull's hand, it was kind of an accident. The Sorcerers of Kahmer Taj don't seem to use portals offensively like that.

Two, it's possible the Power Stone amped Thanos to the point where he is invulnerable to that kind of attack. Improbable, maybe, but possible.

Three, Strange viewed 14 million plus iterations of that battle. It's possible he tried just cutting off Thanos' hand in one (or more) of those iterations, and knew it would (for some reason) fail.