I use Tilex and soft scrub with a scrub brush. Rinse well. Once clean be sure to seal once clean. You won't have to work so hard next time.
Toilet paper and bleach. I saw an advert on YouTube about this and have used it to clean my grout and sealant and it's fantastic. Take 3 squares of toilet paper, fold them longways and twist until tight, like a rope. Place the toilet paper along the grout line and pour over the bleach, not too much just enough to cover paper. Remove after 12 hours and your grout will be shining white.
Whoa! I want to try this!
Try this for cleaning grout: https://www.craftylittlegnome.com/the-best-homemade-grout-cleaner/
This product works really well for me: https://amzn.to/34CtQAD
Hope this Helps! Jeremy - https://do-daddy.com
Whatever method you choose, avoid using vinegar as it will dissolve, damage, or etch the grout.