I need to create a page listing products alphabetically from A to Z and show only the products starting to each letter.
You can change default sorting to Product Name as place of position
Stores > Configuration > Catalog > Catalog > Store Front > Product Listing Sort by
and if you want this to only for particular category then you can change this Category's
Display Settings tab > Default Product Listing Sort By to Product Name
check this screenshot : https://prnt.sc/pj6nre