Shanks would never eat a devil fruit, remember that in the first chapter shanks said to Luffy:

A Pirate strongest weakness is not be able to swim

And Oda makes it clear all the series, not be able to swim is a great problem

But I agree that maybe he knew something we don't..

It would not be strange if this happen

And by the way, he was not a Yonko by the time he lost his arm

Tbh, my guess for Shanks’ (Lucky Roux) finding/looking for the gomu gomu may have been due to the fact it looks almost exactly like the the yami yami and Shanks wanted to prevent BB from getting it.

However, there is always the possibility Shanks just happened upon it after a Pirate battle. Though it’s suspicious to me Shanks was in East Blue for so long for no reason.

It is said in the vivre cards or whatever they are called that Shank's crew mate that chubby guy found the fruit in an enemy ship

Hello? Shanks was in East Blue probably because of Ace. Gol D Roger was his captain and he trusted Shanks with his hat so Shanks was probably looking for Ace to either talk to him or give him the straw hat. Second of all, Shanks did not lose an arm for the Df but for Luffy, as he obvs had conqueror's. He was a skilled swordsman who had went toe to toe with Mihawk and so he coulda killed that sea king easily. Third conqueror's haki is different to the other hakis. Arnament is solid which is like armour and ppl use it to be able to damage Df users and also to increase their power. Katakuri used Observation to move his mochi body around so it would seem like he was a logia when he was moving the insides of his body so no attack hit him. Conqueror's is emitting ur willpower on ppl to do ur bidding. It doesn't really count on the size of the wave cuz that's a bad thing as u could knock out ur own allies. It's about the control. The first step is being able to make everyone around u with a weak will collapse. The second is making a specific person(s) collapse. Third is actually making them submit to ur will. Fourth is making ur will stronger so u can beat other ppl's conqueror's. U can't use a Df to increase ur conqueror's.

Literally no one including Roger's crew knew where Roger's kid was or if it was even a boy or a girl except Garp and Rouge. Even past that Roger's kid was born in South Blue, why in the world would anyone be looking in East Blue for Roger's kid unless Shanks somehow knew Garp had custody of Roger's kid?

Now, it's possible Shanks ended up figuring out Ace was Roger's kid like Whitebeard did. Probably around the time when Shanks actually met Ace in that cave in the New World or started seeing Ace's name in the newspaper. But, definitely not 10 years before the start of the story when pretty much no one outside of that island would have known who Ace was.

If Shanks was actually looking for Roger's kid 12 years before the current story line then it's unlikely he's be looking in East Blue when everyone knew the last place Roger was sighted before turning himself in was South Blue.

This is why I mentioned idk why Shanks was in East Blue back then for such an extended period of time. Reasonable predictions might include: he liked Makino, for the adventure, or he was looking for something most likely to do with Blackbeard. This is Shanks after his initial encounter with Blackbeard where he was scarred and he's been the one warning everyone about Blackbeard before he became the threat that he is now. So, I think it's probably a reasonable idea whatever he was doing in East Blue had something to do with stopping Blackbeard.

However, the likability he was looking for Roger's offspring in East Blue is pretty slim in my opinion considering the circumstances of Ace's birth.