In this passage, the 1858 Wright edition replaced the preposition at with from; the RLDS text followed this reading until the 1908 RLDS edition restored the original at, probably by reference to 𝓟. Here Ammon is saying that the thought that God could have condemned them to eternal destruction almost makes his soul ﬂee. This reference to his soul ﬂeeing seems to mean that this thought made him feel almost like dying or fainting. Ammon is definitely not saying that his soul was trying to ﬂee away from the thought. A similar expression of this idea is found in Alma 29:16: “my soul is carried away even to the separation of it from the body as it were”.
Summary: Maintain in Alma 26:20 the original preposition at in “O my soul almost as it were ﬂeeth at the thought”.