Why I personally believe Goku never (spoiler) against Beerus, and how it can be integrated in super in a way that doesn’t mess with the continuity.

It’s heavily implied Goku achieved SSJ4 before Daima, but said he wasn’t sure it would work in response to Vegeta asking him why he hid it. Based off this, I don’t think it’s something Goku can tap into under normal situations.

From what we know about super saiyan transformations, they come from a response to need, not a desire, and we know that after Buu was defeated there weren’t any villains, so I think this transformation was a result of pure high intensity training. Think back when Gohan achieved SSJ2 for a split second in the hyperbolic time chamber and instantly passed out.

I think Goku pushed himself to the limit in efforts to get stronger and accidentally broke through his limit and caught a glimpse of SSJ4, remember the way he got ultra instinct and how he said he couldn’t do it again at the end of super. He needed a specific trigger.

The first time was Jiren, and the second time was Kefla. For Gohan it was the death of android 16.

What I’m saying is since Daimi takes place in between Buu and Beerus, on top of the fact Vegeta didn’t know about it, I’d say it’s a relatively new transformation for him. Hence, he didn’t know it would work.

Why didn’t Goku use it against Beerus? I’m not gonna make up an answer, the truth is simply because at the time SSJ4 wasn’t canon, so 3 was his limit.

How can it be integrated into super? I’d imagine it’d be something similar to SSJG Vegeta. First time we saw it was in the Broly movie, but we knew he could do it long before because blue is just super saiyan with super saiyan god. He just never bothered to because it’s inferior to blue in terms of power.

At some point in the manga, he’ll just tap into SSJ4 and it probably won’t be explained, it’ll just be to confirm he can access it and Daimi is canon.