Hi @chathuramk,
You can find below css styles in vendor/magento/Magento_Catalog/web/css/source/module/_listings.less line 290 - 295
.products-grid .product-item { width: 100%/3 }
.page-layout-1column .products-grid .product-item { width: 100%/3 }
.page-layout-3columns .products-grid .product-item { width: 100%/3 }
.page-products .products-grid .product-item { width: 100%/3 }
.page-products.page-layout-1column .products-grid .product-item { width: 100%/3 }
.page-products.page-layout-3columns .products-grid .product-item { width: 100%/3 }
So you can copy this file into your theme directory, then change those widths like below.
.products-grid .product-item { width: 100%/4 }
.page-layout-1column .products-grid .product-item { width: 100%/4 }
.page-layout-3columns .products-grid .product-item { width: 100%/4 }
.page-products .products-grid .product-item { width: 100%/4 }
.page-products.page-layout-1column .products-grid .product-item { width: 100%/4 }
.page-products.page-layout-3columns .products-grid .product-item { width: 100%/4 }
If my answer is useful, give kudos & accept as solution.
Best regards
Madhuresan
Bootsgrid