What's the difference from magnesium elemental from magnesium Glycinate/lysinate chelated, sodium bicarbonate, and magnesium oxide?

Diff. absorption and. Magnesium always occurs as a salt in combination with other things such as chloride, oxide, glycine, citrate, taurine etc. Some forms are poorly absorbed; for example magnesium oxide is only 4% absorbed, so it does not raise magnesium much but is a good laxative. The best-absorbed are glycinate and taurate and those amino have benefits. See https://www.organicnewsroom.com/magnesium-supplements/