3.5 was edition I played the most. It was a reason why I quit RPGs for nearly a decade because I hated it so much.
Every time I see another meme about how amazing 3.5 Tarrasque is, I remmember how amogn actual 3.5 players Tarrasque was the biggest joke. It was always brought up as definite proof designers have no idea how to make good monster. It was laughably easy to beat. A wizard could casually solo it, the same abilities people now miss in 3.5 amounted to ribbons. It was a laughingstock, forums had 100+ pages discussions how to fix it and general consensus was it';s beyond saving. It was first proof in 3.5 if you cannot use magic you're only good to roll over and die.
I honestly don't know if everyone claiming 3.5 Tarrasque is such a horrifying monster are trying to rewrite history or unintentionally proving what a broken, unplayable pile of garbage 3.5 was, if it's biggest punching bag is actually dangerous in a different, better designed game.
the usual go to back in the day was to drown it, because it wasnt immune to that in any way. Simply gate it to the plane of water. There was a number of other work arounds like that too.
The best way I've seen to defeat an enemy without killing it is Flesh to Stone, Stone to Mud, Purify Food and Drink, and then boil the water away. That was more for keeping an enemy from being resurrected, but it would be a cool overkill way to get rid of a tarrasque without using Wish.
Killing it by banishing it to another dimension of reality sounds like the epic, high level stuff the Terrasque was made for
i mean, there were plenty of other ways, including things you could do at lower level, that was just the common go to because it required a single high level spell, and usually you fought big T at high level.