These settings are available in system.merge_tree_settings and are autogenerated from the ClickHouse snapshot.
escape_index_filenames
Prior to 26.1 we didn’t escape special symbols in filenames created for secondary indices, which could lead to issues with some characters in index names producing broken parts. This is added purely for compatibility reasons. It should not be changed unless you are reading old parts with indices using non-ascii characters in their names.
escape_variant_subcolumn_filenames
Escape special symbols in filenames created for subcolumns of Variant data type in Wide parts of MergeTree table. Needed for compatibility.