What kind of soap can I use to clean LEGO?
The official guidance from The LEGO group suggests using a mild detergent.

Cleaning your LEGO® bricks is really easy! We recommend that you clean
your LEGO® parts by hand using water no hotter than 104°F / 40°C and a
soft cloth or sponge.** Higher temperatures may affect the quality of
the parts. You can add a mild detergent to the water - please
rinse them well with clear water afterwards and you're done!
A word of warning! Please don't put your LEGO® pieces in the washing
machine or dishwasher, and don't try to dry them in the oven, the
microwave or with a hair dryer. When the bricks get really hot they
may change shape, which means they won't work anymore!

Cleaning your LEGO® bricks
In most cases warm water is enough to clean LEGO bricks, some soap can help remove tougher stains, dirt and smells.
Examples of mild detergent include liquid hand or dish washing soap, as opposed to things like bleach and ammonia which are irritating and corrosive to the skin which may damage bricks.
Mild detergent should be enough to both clean and sanitise.