Based on the given information, the spfli database table should have the following general settings:
"Storage Type" to "Row Store": This setting determines how the data is stored in the SAP HANA database. Row store is suitable for tables that are accessed by primary key or by a small number of columns. Column store is suitable for tables that are accessed by a large number of columns or by complex analytical queries. Since the spfli table is a large table with over one million rows, and this program is the only one in the system that accesses the table, it is likely that the program will use primary key access or simple queries to access the table. Therefore, row store is a better choice than column store for this table12.
"Load Unit" to "Page Loadable": This setting determines how the data is loaded into the memory when the table is accessed. Page loadable means that the data is loaded in pages of 16 KB each, and only the pages that are needed are loaded. Column loadable means that the data is loaded in columns, and only the columns that are needed are loaded. Since the spfli table is a row store table, and this program will run rarely, it is more efficient to use page loadable than column loadable for this table. Page loadable will reduce the memory consumption and the loading time of the table13.

The function find_any_not_of returns the position of the first character in the string val that is not contained in the string sub. If no such character is found, the function returns 0. In this case, the string val contains only the characters A, B, and a, which are all contained in the string sub, so the function returns 0. The other functions return positive values, as follows:
Count_any_of returns the number of occurrences of any character in the string sub within the string val. In this case, it returns 8, since there are 8 A's and B's in val.
Count returns the number of occurrences of the string sub within the string val. In this case, it returns 2, since there are 2 AB's in val.
find_any_of returns the position of the first character in the string val that is contained in the string sub. In this case, it returns 1, since the first character A is in sub. Reference: String Functions - ABAP Keyword Documentation, Examples of String Functions - ABAP Keyword Documentation

SAP recommends that you eliminate the following types of legacy code when you review modifications as part of an SAP S/4HANA system conversion:
Code that now is identical to a standard SAP object. This type of code is redundant and unnecessary, as it does not provide any additional functionality or customization. It can also cause conflicts or errors during the system conversion, as the standard SAP object may have changed or been replaced in SAP S/4HANA. Therefore, you should delete this type of code and use the standard SAP object instead.
Code that can be redesigned as a key user extension. This type of code is usually related to UI or business logic adaptations that can be achieved using the in-app tools provided by SAP S/4HANA. By redesigning this type of code as a key user extension, you can simplify and standardize your code base, reduce maintenance efforts, and avoid compatibility issues during the system conversion. Therefore, you should migrate this type of code to the key user extensibility framework and delete the original code.
The other types of legacy code are not recommended to be eliminated, as they may still be relevant or necessary for your business processes. However, you should still review and adjust them according to the SAP S/4HANA simplification items and best practices. These types of code are:
Code that supports a critical business process. This type of code is essential for your business operations and cannot be easily replaced or removed. However, you should check if this type of code is compatible with SAP S/4HANA, and if not, you should adapt it accordingly. You should also consider if this type of code can be optimized or enhanced using the new features and capabilities of SAP S/4HANA.
Code that has less than 10% usage according to usage statistics. This type of code is rarely used and may not be worth maintaining or converting. However, you should not delete this type of code without verifying its relevance and impact on your business processes. You should also consider if this type of code can be replaced or consolidated with other code that has higher usage or better performance.