If you have the problem to develop any EXCEL-scenarios with SAP i can recommend to install and use nugget ABAP2XLSX.
I've made best experience using this feature for direct EXCEL-Ex- & Import. Thanks people for this development!
Although there is little bug interpreting fix column/lines (class zcl_excel_reader_2007, method load_worksheet) this feature ist very effective and has a very good performance. You need not to care about XML and other stuff.
Forget all about SAP-functions TEXT_CONVERT_XLS_TO_SAP or ALSM_EXCEL_TO_INTERNAL_TABLE and similar. They all use OLE-screnario with restricted and uncontrollable clipboard-functions. Further they all have strict limits using string-containers.
To download this nugget follow this link.
Thanks for further comments and/or discussions in advance.