Starting with the version WooCommerce 8.0 Many changes have been made to increase the optimization of online stores, but some problems have also occurred. Especially at online stores that have products with values of attributes (variations) composed of less than 3 characters. Example: S, M, L, XL, 23, 42, etc. “Please enter 3 or more characters“.
So, if you manage an online store and you can no longer add values of composed variations from one or two characters, the solution below could help you.

I don't know if in the future versions of WooCommerce This 3 -character limitation will remain when adding the terms for attributes, but until then, the simplest solution is to add three spaces (press 3 times the key “Space“) to display all attribute terms.

In my example, to list in search all the terms of the attributes containing “X”, typed two spaces, then “X”.
Momenan this is the only simple method by which you can look for terms of attributes in less than 3 characters in WooCommerce 8.X.