It is a requirement for flex-fuel tunes, that's how they flex. Running E40 always isn't a flex tune, it's an E blend tune.
I think a couple of things of note here:
1) The fuel system should be ok on E40, but you should definitely test, tune and read your logs, or have someone read your logs...
I mean Big Boost, and there's another big name coming with one soon.
https://bigboostturbo.com/collections/a90-a91-gr-supra/products/2020-2-port-supra-pte6466-turbo-kit