Excel 2013 and later has a columnar database capable of handling millions of rows, but not through the standard sheets interface so it loses a lot of the utility people are used to.
Yes, although you can have multiple sheets each with a million rows. Kind of like sharding.
But I’d be fascinated what kind of system spec is required to get good performance on those kind of numbers. I’ve been on a Mac for years, where Excel is crippled by limitations.