You just made the mistake that has led to the confusion! You've assumed that when it said "sabbath day" that it was referring to a Saturday, but you've completely overlooked the words in brackets - "for that sabbath day was an high day". A "High Sabbath" refers to seven specific annual Biblical festivals and rest days. These days, also called "feasts" or "called assemblies," are distinct from the weekly Sabbath and they are based on the Jewish lunar calendar - they can occur on any day of the week.
No, I did not! That particular saturday began the feast of unleavened bread! Thursday night to Friday sunset was passover, and the day of preparation (removing the leaven from houses.
That particular Sabbath (Saturday) was a high Sabbath in that on that Saturday the Feast of Unleavened bread began.
John 19:31
The Jews therefore, because it was the preparation, that the bodies should not remain upon the cross on the
sabbath day, (for that
sabbath day was an
high day,) besought Pilate that their legs might be broken, and that they might be taken away.
Read it using saturday for Sabbath.
...on Saturday, for that Saturday was a High Day......