This is after scrubbing and the grout used to be white. I think it just has to be redone. 
Discussion
I would redo the silicone around the tub by heating it with a hair dryer, using a plastic tool once it’s gooey. https://youtu.be/_DI4hfHM_Hg?si=9ZmediVIP1IZ24_7
In between the tiles you can try grandmas stain remover and a firm toothbrush 
Try bleach yet? Just spray it and come back in an hour. I also like 3M heavy duty brushes you can put some elbow grease behind.
Where the tub meets the tile use a bathroom caulk. Run a piece of painters tape, run a bead, dip finger in windex or use a silicone glove to run your finger across the joint. Pull the tape.
?crop=1xw:1xh;center,top&resize=980:*
Power drill with a brush attachment works well too.
believe it or not, toilet bowl cleaner. clears out serious stains.