Worth mentioning is the use of Kombu seaweed to soften beans. The common narrative is that enzymes in thre Kombu act on the outer bean layers. What I find puzzling about that idea is that enzymes, being proteins, are inactivated by cooking.So I would expect Kombu to work better with a room temperature pre-soak.
What with the variation in bean batches due to farming practices etc., its hard to make definitive statements or know anything. For example, I was surprised to find out soaking is not necessary and may degrade flavor. Likewise the proper use of Kombu maybe was never passed on from the Japanese cooks. Or an erroneous version passed on. Or the whole thing was a non-scientific "belief," like not to stir a pot counter clockwise.

Simple answer, it neutralises acid in the beans if you put it in at the start of the boiling process.😕😕😕

Salt does slow down the cooking. I add salt at the end of the cooking.

I thought this would help. Good luck!

http://whatscookingamerica.net/Vegetables/driedbeantip.htm

Acidic ingredients will prevent beans from softening. So they should be added after the beans have softened.

Acid/PH is a greater factor for beans, and cooking time. This can depend on your tap water. In the south...water has a high lime content. So some localized recipes don't care about salt...as the lime in the water makes them soft. With standardized water systems, and internet moving info from region to to region quickly; some old school advice and recipes are off on such small details--so we're back to square one on adjusting. (Often with high tech PH meters, gram weigh scales, and additions of magical powers to correct and adjust).

Great! Thanks so much for all of your feedback!

According to Cooks Illustrated if you brine the beans before cooking they will have softer skins when cooked. "Why? It has to do with how the sodium ions in salt interact with the cells of the bean skins. As the beans soak, the sodium ions replace some of the calcium and magnesium ions in the skins. Because sodium ions are more weakly charged than calcium and magnesium ions, they allow more water to penetrate into the skins, leading to a softer texture. During soaking, the sodium ions will only filter partway into the beans, so their greatest effect is on the cells in the outermost part of the beans."

Split decision;
According to Steve Sando, the bean guru at Rancho Gordo (http://www.ranchogordo.com/html/rg_cook_beans_primer.htm) you should salt late in the cooking process and allow time for the salt to be absorbed before tasting to be sure it's the right amount. Salt slows the softening.
But Harold McGee, an authoritative source on the science of cooking, says to salt the soaking water.

The common wisdom is salt should be added at the last of the cooking. But I haven't seen any side-by-side tests.

I do know that for older beans, a pinch of baking soda in the water speeds up the softening process, I use that for stubborn beans that just aren't getting soft.

Be careful with the baking soda...just a pinch, it's a fine line last resort trick to soften/speed beans that don't cook quickly. Too much it leaches out flavor and vitamins.