The Uniswap Labs web app will only offer the ability to route through UniswapX when the value of the swap is above a certain threshold.
The swap minimum depends on the Network Costs of the swap, which is different and changes for every swap.
If value of the swap is below this threshold, then the Uniswap web app will automatically route swaps through the liquidity pools on Uniswap v2 and v3.
Note: Swaps will automatically be routed through the liquidity pools on Uniswap v2 and v3 if a better price is available.
Updated