How can I change the size and layout of my Store Products on Mobile/Tablet only?

You mean change to 2 items/row on tablet/mobile?

Add to Design > Custom CSS

/* Product 2 columns mobile tablet */
@media screen and (max-width:991px) {
	.products.collection-content-wrapper .list-grid {
    display: grid;
    grid-template-columns: repeat(2,minmax(0,1fr));
    grid-column-gap: 10px;
}
}

That's AWESOME!! So cool thank you!

I tried this and looks great. However, I might use this layout once I get more products made.

Could you help me please by making the products single row but smaller showcase like the second image above?

Thank you!