Non bleach tile and bath cleaner!
I picked up this tip and it has been so easy and successful . Use toilet bowl clinging gel and pour it on the grout. Leave for 20 mins. Sometimes you might need to scrub loose the dirt with a toothbrush. Rinse clean. Great smell too .
These are some good ideas for cleaning grout. The suggestion is to use milder cleaning solutions first. Super strong cleaning solutions can eat up your grout. https://www.google.com/amp/s/amp.realsimple.com/home-organizing/how-to-clean-grout%3fsource=dam
Home Depot has grout paint. It's easy but tedious.
The best way is the contact a steam cleaning company and have them steam the group. Another idea is make a paste with baking soda ad peroxide and clean the grout with a toothbrush.