I believe the "Sheet Border - Title Blocks" nomenclature was for 2018 and older. The folders seem to have been renamed since then to match how things are named in the program.   If you're looking to save the entire "Title Block Border" object style (which can include sheet size, margins, title block geometry, project/sheet data, etc.), then the necessary subfolder is:   Libraries > Objects Styles > Title Block Border (put file in this subfolder on your hard drive).
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