Liberalism was the original leftism: see the French revolutionary National Assembly. It doesn't intrinsically have anything to do with capitalism. In general, liberalism is neither left nor right. It promotes individualism. Historically, it progressed from humanism.

leftism begins at anti-capitalism

Not the political science definition.

General definitions & the historical development of liberalism are academic.

liberalism, political doctrine that takes protecting and enhancing the freedom of the individual to be the central problem of politics. Liberals typically believe that government is necessary to protect individuals from being harmed by others, but they also recognize that government itself can pose a threat to liberty.

Some of the earliest liberal practices are found in the US Declaration of Independence, which predates the French revolution spreading the practice of liberal ideals throughout Europe. The US declaration pretty much rehashes core tenets of liberal philosophy

• inherent equality of individuals
• universal individual rights & liberties
• consent of the governed (governments exist for the people who have a right to change & replace them, & authority is legitimate only when it protects those liberties).

Note how capitalism isn't mentioned anywhere: it's nonessential. Capitalism predates & isn't liberalism. Liberalism is moral & political philosophy, not an economic one.

The philosophy is a natural progression of humanist philosophies from the Renaissance through the Protestant Reformation & the Enlightenment that stress the importance of individuality, secular reasoning, & tolerance over dogma & subservience to unaccountable authority. To address unaccountable authority based on dogma & traditions, English & French philosophers defined legitimate authority based on humanist morality pretty much as expressed in the US declaration. They argued that political systems thrive better with limits & duties on authority & an adversarial system of institutional competition whether in separation of powers, adversarial law system with habeas corpus & right to jury trial, competitive elections, dialogue, or economic competition.