If you have a RPI4 you can run a 64bit OS as the processors are the arm64/AArch64. However, you can't upgrade your current install from 32bit to 64bit but need to start anew (get a new SD card and install the 64bit OS). A 64-bit OS can run 32-bit programs (Windows does it, MacOS used to, Linux does by having the 32bit libraries installed in a separate area).

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