As someone familiar with how Matsa has been kept historically and today, the Jews in 1st century Israel would have probably understood that Matsa was a non-working day. Businesses would have been closed. Buying and selling was prohibited. You are correct that Matsa is not called a "Sabbath" in the Tanakh. But it is called a "Shabbaton". This word probably means "lesser Sabbath", or "half Sabbath". Today, Orthodox Jews keep Shabbaton the same way as the weekly Sabbath, although they know these are different. Because of the uncertainty of what was allowed or not allowed on a Shabbaton, they made a rule to just keep it as Shabbat.
Now, if you look in the Greek, you will see the untranslated Hebrew word "Shabbaton" in Mark 15:42 προσάββατον. This confirms that the "preparation day" according to Mark, was in fact a preparation for a Shabbaton(προσάββατον), and not a preparation for the weekly Sabbath(σάββατ).
This obvious fact is easily revealed by the Greek text. Somewhere in Church history, someone, probably a gentile, confused this word προσάββατον as being a synonym of προσάββατ. And the error of a Friday crucifixion has been passed down to this day.
Again, it is impossible to get 3 days and 3 nights as Yeshua said, from a Friday crucifixion.
Again, Mark 15:42 tells us this was a preparation for a Shabbaton, not a preparation for the weekly Shabbat.
Blessings