What type of grout is there now? Does the shower drain properly? Grout is not nor was intended to be waterproof. Just changing the grout may not fix your issue.

I have 1 x1 tile with regular white sanded grout. It is graded properly. I wish I had a solid shower pan instead like my old house.

The mold is an issue needing attention. Poor ventilation is the issue so better venting will help that. White grout discolors very quickly and why was sanded used ? I would be very leery of someone digging into grout on my shower floor in case waterproofing is damaged . Epoxy grout is not going to fix the mold but is stain resistant and if done right waterproof

Thank you. I have a huge exhaust fan. Probably not leaving it on long enough.

Epoxy grout will have surface mold too. It's the skin cells and moisture that feed the mold. You have to dry the space after use, and clean regularly.

Than you all. i thought weekly cleaning was enough. It only in corners so it has to be because I'm not drying it down and/or running the exhaust fan long enough.