> My M1 MacBook Air took about 11 seconds to load and save it each week! Though curiously if I save it as a classic Excel file, it loads on my Dell Pentium III in… wait, only 14 seconds? That’s probably worth its own post.

I guess the old format (xls) is quicker as it is not XML-like structure, rather than memory-dump of running excel process? I might be wrong here.