The theme that runs through the whole “suffering servant” cycle John 12:41 mentions is “glory.”

So a paraphrase would be something like…

‘Isaiah said these things about the glory of Messiah (Isa 4:2; 49:5LXX; 52:13-15LXX; 53:1; 6:3, 10) because he saw Messiah’s future glory.’

Thus, Jesus rightly says “Abraham rejoiced to see my day.” John 8:56.

Again, nothing to do with a literal, pre-existent person; let alone the 2nd member of a 3-in-1 God!

Also of note is the identity of “the servant of Yahweh” as originally the nation of Israel itself (Isa 41:8; 45:4; 49:3, a preexistent being?!)! And the nation is portrayed as a suffering, human being called:

• “the branch of Yahweh” (4.2);
• “who fears Yahweh” (11.3);
• who “grows up like a young plant before Yahweh” (53.2);
• and ultimately will bear all the sins of all peoples because Yahweh’s will is to “crush” him, i.e., cause him pain/suffering (53.2, 6)!

Nonsensical, not to mention blasphemous, to somehow read this figure as Yahweh Himself!