Here’s the approach I would take, assuming you have some spare tile.
Hold the tile pieces in place so the points touch.
Eyeball the angle and draw two lines, one on each piece, making them about 1/8” apart so they’re parallel to one another and look like they’re splitting the angle.
Cut to those lines on the tile saw.
Put the pieces back in place, butting them together where you made the cut.
Draw two more lines, adjusting a bit if the angle on the first try wasn’t perfect.
Cut the lines, butt them together and see how it looks.
It doesn’t have to be completely precise since you’ll want to leave a gap and grout it anyway.