If you switched to plant milk and your morning foam fell apart, you did not lose your technique. Every one of these liquids builds bubbles differently, and two of the popular ones barely build them at all.
In dairy, protein does that work. Plant milks vary enormously in how much protein they carry and what shape it is in, so the same thirty seconds of whisking gives wildly different results in each cup.
Soy carries the most protein of the common plant milks and foams closest to dairy. Its weakness is acid: pour cold soy into hot espresso and it can curdle into flecks. Warm the soy first and pour slowly and it holds. A handheld whisk from a small-appliance catalog like https://peach-street.net/ handles soy with no special technique.
Oat milk is protein-poor, yet it foams beautifully because the starches and gums give the liquid body, and barista versions add a little oil and a phosphate buffer that keeps it from splitting in coffee. That is what the word barista on the carton actually means.
Almond milk is mostly water with a little ground nut and a stabilizer. There is very little there to trap air, so you get big loose bubbles that vanish in a minute. Barista almond blends improve it. Standard almond milk will not behave.
Coconut beverage foams a little because of its fat and gums, but the flavor takes over the drink. Rice milk is thin and sweet and does not foam in any useful way.
Plant milks scorch and split at a lower temperature than cow milk. Aim for hot to the touch through the cup wall, not steaming. Overheated oat milk turns thin and tastes like wet cardboard.
Cold liquid holds air better. Whisk cold, then heat, or heat gently and whisk immediately, and drink it within a minute or two. Plant foam has a much shorter life than dairy foam.
Acidic coffee attacks weak protein structures. Pour the coffee first, then spoon the foam on top instead of pouring it in.
Soy and barista oat will get you a thick, spoonable cap. Almond and rice will not, at any price, with any device. Choose the carton before you blame the tool.
