PSA: When liquid soap (including body wash, shampoo, shower gel, ...) says it's "99% biodegradable", that is meaningless greenwashing.
Liquid soaps are mostly water by volume, so *all* of them hit high percentages here, whether they advertise it or not. The problem is the 1% of additives, which are often plastics.
If you want something that is environmentally better than average, you need to look for *100%* biodegradable soaps.
@joepie91 Why would one add plastics to a soap?
(The old commonly greenwashed issue was, some detergents, particulary a number of types marketed for laundry, would be so biodegradable that, dumped to bodies of freshwater, they'd cause aggressive blooming of water plants.)
@riley In shampoo, for example, plastics are sometimes used to produce a 'shiny' film on your hair. Shower gel sometimes uses it for mixed-in 'massage beads'. And so on. The exact application varies.
Speaking of which, it's very easy to make your own liquid soap from a bar of soap. You literally just crush/shave/whatever the bar of soap, and drop it into a big pot of boiling water and let it boil for a while. Ta-da, liquid soap.
Exact ratio may vary by soap, I don't remember the rule of thumb but it should be pretty easy to find.
The consistency will be less nice than commercial liquid soap, but if you can only find biodegradable soap in bar form, this is one way to turn it liquid, and it does in fact work with standard liquid soap dispensers.
(Do keep in mind that you will need to wash the pot thoroughly after use. I'd recommend doing this stuff in batches so that you only have to clean it once for a big supply.)