Internally I've a feeling an input type number is going to be using the Number type, and not the bigint. You will likely need to just use a normal string input, and handle the increment, decrement manually..
Below is an example, you will probably want to extend to handle keypress for number etc, you could alter the look and feel to make it appear like a number input etc.
const [iBig, iNorm] = document.querySelectorAll('input');
iNorm.value = 10000000000000000000000;
const [btnUp, btnDown] = [...document.querySelectorAll('button')];
btnUp.addEventListener('click', () => {
iBig.value = (BigInt(iBig.value) + 1n).toString();
});
btnDown.addEventListener('click', () => {
iBig.value = (BigInt(iBig.value) - 1n).toString();
});
<p>Handle our bigint's manually.</p>
<input
value="10000000000000000000000" style="width: 200px"/>
<button>⬆</button>
<button>⬇</button>
<br/>
<p>Normal input.. with such a big number does not work</p>
<input
value="" style="width: 200px" type="number"/>