first of all, I understand that it's a word used to horshoe theory socialism and fascism as equally evil (and thus apologizing for the horribleness of fascism)

the history of the term is as follows:

The terms “totalitarian” and “totalitarianism” entered political debate in the 1920s, primarily in reference to Italian fascism. They moved into academic debate in the late 1940s and 1950s with a distinct focus on Germany. They gained popular and academic currency during the Cold War, mostly in reference to the Soviet Union. Concurrently, they became a staple of secondary and postsecondary teaching and of media debate with works like Arthur Koestler’s Darkness at Noon and, more prominently, George Orwell’s 1984, which made the image of the ideologically driven, mind-altering police state pervasive. In popular parlance, totalitarianism lumped together the two most prominent European dictatorships of the 1930s and 1940s, Nazi Germany and the Stalinist Soviet Union, as expressions of absolute evil rather than any particular form of rule. The two regimes were juxtaposed with the “righteous” path of liberal democracy, both as a way of life and as a form of governance.

and another quote:

"To place Russian communism and Nazi-fascism on the same moral place, in the measure that both are totalitarian, is superficial at best; fascism at worst. Anyone who insist on this comparison could very well be considered a democrat, but deep in their heart a fascist is already there, and naturally they will only fight fascism in a superficial and hypocritical way, while they save all their hatred for communism." - Domenico Losurdo, Stalin: History and Critique of a Black Legend.

I couldn’t find any Marxist definitions of totalitarianism so I’ll use the definition as described by political scientists and influential scholars on totalitarianism Carl Joachim Friedrich and Zbigniew Brzezinski (later famous as Jimmy Carter’s National Security Advisor). According to Friedrich and Brzezinski, in order for a state to be totalitarian, one must have the following six mutually exclusive characteristics:

1. Elaborate guiding ideology.
2. Single mass party, generally led by a dictator.
3. System of terror, using such instruments as violence and secret police.
4. Monopoly on weapons.
5. Monopoly on the means of communication.
6. Central direction and control of the economy through state planning.

Finally I'm going to attach an amalgamation of good comments I found somewhere:

It's hard to convince comfortable liberals that they already live in a dystopian security state hellscape, because they are in the part where the grass is green and the wind smells nice.

There are more people in prison in the US right now than at the height of the Great Purge when the USSR's prison population tripled for a couple years before going back to its normal levels as people were amnestied or had their records expunged en masse. So in the US, the number of incarcerated people is worse in a sustained way, than the worst spike in incarceration in what liberals will uphold as the gold standard of communist oppression, the gulag system. This is not to mention the additional millions of people on parole or otherwise "in the system" who are subject to monitoring, check-ins, restricted movement, etc etc etc. Liberals tend not to know anybody in these situations, or if they do they ostracize and marginalize these people. For working people and oppressed communities, it's weird if you don't know somebody who has been caught up in the system, because the system preys on us.

What part of life in the capitalist west is un-totalized by capitalism? It's in healthcare, education, recreation and sports, culture and arts, even how the sciences are pursued. Hard to imagine a more totalitarian experience. If communism is totalitarian, which I reject as a nonsense term that obscures rather than clarifies, then at least it is a totalitarianism where all the wealth of society doesn't accrue to an owner-oppressor class.

It really bothers me that they never apply the idea of "totalitarianism" to colonialism. What could possibly more totalitarian than slave catchers, human zoos, horrific pseudo science experimentation on dehumanized people, and all the other horrors that go along with it.