Alioth was enchanted by Loki and Loki, but not without the sacrifice of the Loki we all mourn(*).
In the Void, all the magic Loki, Loki, Loki, perhaps the little green Loki, Loki, Loki, and perhaps the other Loki(s) from the rival group they fought in the basement... were available. Not in the TVA but in the Void. So, perhaps the Infinity Stones could be used as well. Loki (the main one, say) can use Infinity Stones with his bare hands, so perhaps he could use the 6 at the same time.
There were lots and lots of Infinity Stones stored in a little drawer in the first episode, and there was Mobius who escaped from the Void using a tempad.
A perhaps useful reasoning would be:
- Go to the tempad, back to the offices.
- Seek the Infinity Stones in the drawer. Take 6 of them, distinct.
- Keep the tempad in the suit, as Sylvie (Loki) did, and also keep the stones, look for a pruning rod or a guard who has one, and get pruned, back to the void with the 6 Infinity Stones to use against Alioth.
Is there any reason (an in-universe explanation, and nothing like Wanda's "the director did not know who was Mephisto") why Loki (the main one) did not consider this (e.g. was it proven that infinity stones would not be useful against Alioth)?
(*) yes, that was a very sad night to me.