This is a really nice guide to the BASIC 4.5 extension

BASIC 4.5 is a merged product from M&T 64er, 1990/06 – Ein basic für alle“ by Michael Schimek (BASIC 3.5 on C64). The BASIC 4.5 extends the BASIC 3.5 for C64 by Robert Tümmers (DG5KR) in 2020.