How can a house across the street with less sq ftg, smaller lot, etc be valued 66k more than my home

The Zestimate can be difficult to figure out, and there are lots of examples where it is wildly inaccurate.  That's why it (and other automated valuation tools) are rarely used or considered in real estate transactions today.

There are other automated tools, available on websites for a flat fee, that will often give a similar result.  They all have fairly complicated calculations that combine lots of data, recent sales, multiple listing service (MLS), tax assessor data, and more.  Sometimes even when all that data is correct the result is way off the mark.  Other times some of the listing data is inaccurate and that makes the Zestimate inaccurate as well.

Thankfully, for real estate transactions most lenders require a human appraiser to look at the property, so they get a much more accurate result (almost always, that is).  As a Ohio Real Estate Broker I've seen some appraisals that are way off, but that is the exception to the rule.  Most appraisers do an excellent job of valuing and pricing real estate.