Difference between screens 1 and 2 and screen 3 is the table.
Looks like you created a new number y_1 thats overriding any other y_1 in the graph. That includes your tangent line
If you name it something else in the graph you should be good to go.
Pro tip: if its just for a visual you don’t actually need y= in this case. OOoooh and you can use F’(a) to save you a line and some work! Desmos | Graphing Calculator